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23 Indexed Collections

23.1 Array Objects

Arrays are exotic objects that give special treatment to a certain class of property names. See 10.4.2 for a definition of this special treatment.

23.1.1 The Array Constructor

The Array constructor:

  • is %Array%.
  • is the initial value of the "Array" property of the global object.
  • creates and initializes a new Array when called as a constructor.
  • also creates and initializes a new Array when called as a function rather than as a constructor. Thus the function call Array(…) is equivalent to the object creation expression new Array(…) with the same arguments.
  • is a function whose behaviour differs based upon the number and types of its arguments.
  • may be used as the value of an extends clause of a class definition. Subclass constructors that intend to inherit the exotic Array behaviour must include a super call to the Array constructor to initialize subclass instances that are Array exotic objects. However, most of the Array.prototype methods are generic methods that are not dependent upon their this value being an Array exotic object.

23.1.1.1 Array ( ...values )

This function performs the following steps when called:

  1. If NewTarget is undefined, let newTarget be the active function object; else let newTarget be NewTarget.
  2. Let proto be ? GetPrototypeFromConstructor(newTarget, "%Array.prototype%").
  3. Let numberOfArgs be the number of elements in values.
  4. If numberOfArgs = 0, return ! ArrayCreate(0, proto).
  5. If numberOfArgs = 1, then
    1. Let length be values[0].
    2. Let array be ! ArrayCreate(0, proto).
    3. If length is not a Number, then
      1. Perform ! CreateDataPropertyOrThrow(array, "0", length).
      2. Let intLength be 1𝔽.
    4. Else,
      1. Let intLength be ! ToUint32(length).
      2. If SameValueZero(intLength, length) is false, throw a RangeError exception.
    5. Perform ! Set(array, "length", intLength, true).
    6. Return array.
  6. Assert: numberOfArgs ≥ 2.
  7. Let array be ? ArrayCreate(numberOfArgs, proto).
  8. Let k be 0.
  9. Repeat, while k < numberOfArgs,
    1. Let propertyKey be ! ToString(𝔽(k)).
    2. Let itemK be values[k].
    3. Perform ! CreateDataPropertyOrThrow(array, propertyKey, itemK).
    4. Set k to k + 1.
  10. Assert: The mathematical value of array's "length" property is numberOfArgs.
  11. Return array.

23.1.2 Properties of the Array Constructor

The Array constructor:

  • has a [[Prototype]] internal slot whose value is %Function.prototype%.
  • has a "length" property whose value is 1𝔽.
  • has the following properties:

23.1.2.1 Array.from ( items [ , mapper [ , thisArg ] ] )

This function performs the following steps when called:

  1. Let ctor be the this value.
  2. If mapper is undefined, then
    1. Let mapping be false.
  3. Else,
    1. If IsCallable(mapper) is false, throw a TypeError exception.
    2. Let mapping be true.
  4. Let usingIterator be ? GetMethod(items, %Symbol.iterator%).
  5. If usingIterator is not undefined, then
    1. If IsConstructor(ctor) is true, then
      1. Let array be ? Construct(ctor).
    2. Else,
      1. Let array be ! ArrayCreate(0).
    3. Let iteratorRecord be ? GetIteratorFromMethod(items, usingIterator).
    4. Let k be 0.
    5. Repeat,
      1. If k ≥ 253 - 1, then
        1. Let error be ThrowCompletion(a newly created TypeError object).
        2. Return ? IteratorClose(iteratorRecord, error).
      2. Let propertyKey be ! ToString(𝔽(k)).
      3. Let next be ? IteratorStepValue(iteratorRecord).
      4. If next is done, then
        1. Perform ? Set(array, "length", 𝔽(k), true).
        2. Return array.
      5. If mapping is true, then
        1. Let mappedValue be Completion(Call(mapper, thisArg, « next, 𝔽(k) »)).
        2. IfAbruptCloseIterator(mappedValue, iteratorRecord).
      6. Else,
        1. Let mappedValue be next.
      7. Let defineStatus be Completion(CreateDataPropertyOrThrow(array, propertyKey, mappedValue)).
      8. IfAbruptCloseIterator(defineStatus, iteratorRecord).
      9. Set k to k + 1.
  6. NOTE: items is not iterable so assume it is an array-like object.
  7. Let arrayLike be ! ToObject(items).
  8. Let length be ? LengthOfArrayLike(arrayLike).
  9. If IsConstructor(ctor) is true, then
    1. Let array be ? Construct(ctor, « 𝔽(length) »).
  10. Else,
    1. Let array be ? ArrayCreate(length).
  11. Let k be 0.
  12. Repeat, while k < length,
    1. Let propertyKey be ! ToString(𝔽(k)).
    2. Let kValue be ? Get(arrayLike, propertyKey).
    3. If mapping is true, then
      1. Let mappedValue be ? Call(mapper, thisArg, « kValue, 𝔽(k) »).
    4. Else,
      1. Let mappedValue be kValue.
    5. Perform ? CreateDataPropertyOrThrow(array, propertyKey, mappedValue).
    6. Set k to k + 1.
  13. Perform ? Set(array, "length", 𝔽(length), true).
  14. Return array.
 Note

This method is an intentionally generic factory method; it does not require that its this value be the Array constructor. Therefore it can be transferred to or inherited by any other constructors that may be called with a single numeric argument.

23.1.2.2 Array.fromAsync ( items [ , mapper [ , thisArg ] ] )

This async function performs the following steps when called:

  1. Let ctor be the this value.
  2. Let mapping be false.
  3. If mapper is not undefined, then
    1. If IsCallable(mapper) is false, throw a TypeError exception.
    2. Set mapping to true.
  4. Let iteratorRecord be undefined.
  5. Let usingAsyncIterator be ? GetMethod(items, %Symbol.asyncIterator%).
  6. If usingAsyncIterator is undefined, then
    1. Let usingSyncIterator be ? GetMethod(items, %Symbol.iterator%).
    2. If usingSyncIterator is not undefined, then
      1. Set iteratorRecord to CreateAsyncFromSyncIterator(? GetIteratorFromMethod(items, usingSyncIterator)).
  7. Else,
    1. Set iteratorRecord to ? GetIteratorFromMethod(items, usingAsyncIterator).
  8. If iteratorRecord is not undefined, then
    1. If IsConstructor(ctor) is true, then
      1. Let array be ? Construct(ctor).
    2. Else,
      1. Let array be ! ArrayCreate(0).
    3. Let k be 0.
    4. Repeat,
      1. If k ≥ 253 - 1, then
        1. Let error be ThrowCompletion(a newly created TypeError object).
        2. Return ? AsyncIteratorClose(iteratorRecord, error).
      2. Let propertyKey be ! ToString(𝔽(k)).
      3. Let nextResult be ? Call(iteratorRecord.[[NextMethod]], iteratorRecord.[[Iterator]]).
      4. Set nextResult to ? Await(nextResult).
      5. If nextResult is not an Object, throw a TypeError exception.
      6. Let done be ? IteratorComplete(nextResult).
      7. If done is true, then
        1. Perform ? Set(array, "length", 𝔽(k), true).
        2. Return array.
      8. Let nextValue be ? IteratorValue(nextResult).
      9. If mapping is true, then
        1. Let mappedValue be Completion(Call(mapper, thisArg, « nextValue, 𝔽(k) »)).
        2. IfAbruptCloseAsyncIterator(mappedValue, iteratorRecord).
        3. Set mappedValue to Completion(Await(mappedValue)).
        4. IfAbruptCloseAsyncIterator(mappedValue, iteratorRecord).
      10. Else,
        1. Let mappedValue be nextValue.
      11. Let defineStatus be Completion(CreateDataPropertyOrThrow(array, propertyKey, mappedValue)).
      12. IfAbruptCloseAsyncIterator(defineStatus, iteratorRecord).
      13. Set k to k + 1.
  9. Else,
    1. NOTE: items is neither async iterable nor iterable so assume it is an array-like object.
    2. Let arrayLike be ! ToObject(items).
    3. Let length be ? LengthOfArrayLike(arrayLike).
    4. If IsConstructor(ctor) is true, then
      1. Let array be ? Construct(ctor, « 𝔽(length) »).
    5. Else,
      1. Let array be ? ArrayCreate(length).
    6. Let k be 0.
    7. Repeat, while k < length,
      1. Let propertyKey be ! ToString(𝔽(k)).
      2. Let kValue be ? Get(arrayLike, propertyKey).
      3. Set kValue to ? Await(kValue).
      4. If mapping is true, then
        1. Let mappedValue be ? Call(mapper, thisArg, « kValue, 𝔽(k) »).
        2. Set mappedValue to ? Await(mappedValue).
      5. Else,
        1. Let mappedValue be kValue.
      6. Perform ? CreateDataPropertyOrThrow(array, propertyKey, mappedValue).
      7. Set k to k + 1.
    8. Perform ? Set(array, "length", 𝔽(length), true).
    9. Return array.
 Note

This method is an intentionally generic factory method; it does not require that its this value be the Array constructor. Therefore it can be transferred to or inherited by any other constructors that may be called with a single numeric argument.

23.1.2.3 Array.isArray ( arg )

This function performs the following steps when called:

  1. Return ? IsArray(arg).

23.1.2.4 Array.of ( ...items )

This method performs the following steps when called:

  1. Let length be the number of elements in items.
  2. Let lengthNumber be 𝔽(length).
  3. Let ctor be the this value.
  4. If IsConstructor(ctor) is true, then
    1. Let array be ? Construct(ctor, « lengthNumber »).
  5. Else,
    1. Let array be ? ArrayCreate(length).
  6. Let k be 0.
  7. Repeat, while k < length,
    1. Let kValue be items[k].
    2. Let propertyKey be ! ToString(𝔽(k)).
    3. Perform ? CreateDataPropertyOrThrow(array, propertyKey, kValue).
    4. Set k to k + 1.
  8. Perform ? Set(array, "length", lengthNumber, true).
  9. Return array.
 Note

This method is an intentionally generic factory method; it does not require that its this value be the Array constructor. Therefore it can be transferred to or inherited by other constructors that may be called with a single numeric argument.

23.1.2.5 Array.prototype

The value of Array.prototype is the Array prototype object.

This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: false }.

23.1.2.6 get Array [ %Symbol.species% ]

Array[%Symbol.species%] is an accessor property whose set accessor function is undefined. Its get accessor function performs the following steps when called:

  1. Return the this value.

The value of the "name" property of this function is "get [Symbol.species]".

Note

Array prototype methods normally use their this value's constructor to create a derived object. However, a subclass constructor may over-ride that default behaviour by redefining its %Symbol.species% property.

23.1.3 Properties of the Array Prototype Object

The Array prototype object:

  • is %Array.prototype%.
  • is an Array exotic object and has the internal methods specified for such objects.
  • has a "length" property whose initial value is +0𝔽 and whose attributes are { [[Writable]]: true, [[Enumerable]]: false, [[Configurable]]: false }.
  • has a [[Prototype]] internal slot whose value is %Object.prototype%.
Note

The Array prototype object is specified to be an Array exotic object to ensure compatibility with ECMAScript code that was created prior to the ECMAScript 2015 specification.

23.1.3.1 Array.prototype.at ( index )

  1. Let obj be ? ToObject(this value).
  2. Let length be ? LengthOfArrayLike(obj).
  3. Let k be ? ToAbsoluteIndex(index, length).
  4. If k < 0 or k ≥ length, return undefined.
  5. Return ? Get(obj, ! ToString(𝔽(k))).

23.1.3.2 Array.prototype.concat ( ...items )

This method returns an array containing the array elements of the object followed by the array elements of each argument.

It performs the following steps when called:

  1. Let obj be ? ToObject(this value).
  2. Let array be ? ArraySpeciesCreate(obj, 0).
  3. Let nextIndex be 0.
  4. Prepend obj to items.
  5. For each element item of items, do
    1. Let spreadable be ? IsConcatSpreadable(item).
    2. If spreadable is true, then
      1. Let length be ? LengthOfArrayLike(item).
      2. If nextIndex + length > 253 - 1, throw a TypeError exception.
      3. Let sourceIndex be 0.
      4. Repeat, while sourceIndex < length,
        1. Let propertyKey be ! ToString(𝔽(sourceIndex)).
        2. Let exists be ? HasProperty(item, propertyKey).
        3. If exists is true, then
          1. Let subElement be ? Get(item, propertyKey).
          2. Perform ? CreateDataPropertyOrThrow(array, ! ToString(𝔽(nextIndex)), subElement).
        4. Set nextIndex to nextIndex + 1.
        5. Set sourceIndex to sourceIndex + 1.
    3. Else,
      1. NOTE: item is added as a single item rather than spread.
      2. If nextIndex ≥ 253 - 1, throw a TypeError exception.
      3. Perform ? CreateDataPropertyOrThrow(array, ! ToString(𝔽(nextIndex)), item).
      4. Set nextIndex to nextIndex + 1.
  6. Perform ? Set(array, "length", 𝔽(nextIndex), true).
  7. Return array.

The "length" property of this method is 1𝔽.

Note 1

The explicit setting of the "length" property in step 6 is intended to ensure the length is correct when the final non-empty element of items has trailing holes or when array is not a built-in Array.

 Note 2

This method is intentionally generic; it does not require that its this value be an Array. Therefore it can be transferred to other kinds of objects for use as a method.

23.1.3.2.1 IsConcatSpreadable ( obj )

The abstract operation IsConcatSpreadable takes argument obj (an ECMAScript language value) and returns either a normal completion containing a Boolean or a throw completion. It performs the following steps when called:

  1. If obj is not an Object, return false.
  2. Let spreadable be ? Get(obj, %Symbol.isConcatSpreadable%).
  3. If spreadable is not undefined, return ToBoolean(spreadable).
  4. Return ? IsArray(obj).

23.1.3.3 Array.prototype.constructor

The initial value of Array.prototype.constructor is %Array%.

23.1.3.4 Array.prototype.copyWithin ( target, start [ , end ] )

Note 1

The end argument is optional. If it is not provided, the length of the this value is used.

 Note 2

If target is negative, it is treated as length + target where length is the length of the array. If start is negative, it is treated as length + start. If end is negative, it is treated as length + end.

This method performs the following steps when called:

  1. Let obj be ? ToObject(this value).
  2. Let length be ? LengthOfArrayLike(obj).
  3. Let to be ? ToClampedIndex(target, length).
  4. Let from be ? ToClampedIndex(start, length).
  5. If end is undefined, let final be length; else let final be ? ToClampedIndex(end, length).
  6. Let count be min(final - from, length - to).
  7. If from < to and to < from + count, then
    1. Let direction be -1.
    2. Set from to from + count - 1.
    3. Set to to to + count - 1.
  8. Else,
    1. Let direction be 1.
  9. Repeat, while count > 0,
    1. Let fromKey be ! ToString(𝔽(from)).
    2. Let toKey be ! ToString(𝔽(to)).
    3. Let fromPresent be ? HasProperty(obj, fromKey).
    4. If fromPresent is true, then
      1. Let fromValue be ? Get(obj, fromKey).
      2. Perform ? Set(obj, toKey, fromValue, true).
    5. Else,
      1. Assert: fromPresent is false.
      2. Perform ? DeletePropertyOrThrow(obj, toKey).
    6. Set from to from + direction.
    7. Set to to to + direction.
    8. Set count to count - 1.
  10. Return obj.
 Note 3

This method is intentionally generic; it does not require that its this value be an Array. Therefore it can be transferred to other kinds of objects for use as a method.

23.1.3.5 Array.prototype.entries ( )

This method performs the following steps when called:

  1. Let obj be ? ToObject(this value).
  2. Return CreateArrayIterator(obj, key+value).

23.1.3.6 Array.prototype.every ( callback [ , thisArg ] )

Note 1

callback should be a function that accepts three arguments and returns a value that is coercible to a Boolean value. every calls callback once for each element present in the array, in ascending order, until it finds one where callback returns false. If such an element is found, every immediately returns false. Otherwise, every returns true. callback is called only for elements of the array which actually exist; it is not called for missing elements of the array.

If a thisArg parameter is provided, it will be used as the this value for each invocation of callback. If it is not provided, undefined is used instead.

callback is called with three arguments: the value of the element, the index of the element, and the object being traversed.

every does not directly mutate the object on which it is called but the object may be mutated by the calls to callback.

The range of elements processed by every is set before the first call to callback. Elements which are appended to the array after the call to every begins will not be visited by callback. If existing elements of the array are changed, their value as passed to callback will be the value at the time every visits them; elements that are deleted after the call to every begins and before being visited are not visited. every acts like the “for all” quantifier in mathematics. In particular, for an empty array, it returns true.

This method performs the following steps when called:

  1. Let obj be ? ToObject(this value).
  2. Let length be ? LengthOfArrayLike(obj).
  3. If IsCallable(callback) is false, throw a TypeError exception.
  4. Let k be 0.
  5. Repeat, while k < length,
    1. Let propertyKey be ! ToString(𝔽(k)).
    2. Let kPresent be ? HasProperty(obj, propertyKey).
    3. If kPresent is true, then
      1. Let kValue be ? Get(obj, propertyKey).
      2. Let testResult be ToBoolean(? Call(callback, thisArg, « kValue, 𝔽(k), obj »)).
      3. If testResult is false, return false.
    4. Set k to k + 1.
  6. Return true.
 Note 2

This method is intentionally generic; it does not require that its this value be an Array. Therefore it can be transferred to other kinds of objects for use as a method.

23.1.3.7 Array.prototype.fill ( value [ , start [ , end ] ] )

Note 1

The start argument is optional. If it is not provided, +0𝔽 is used.

The end argument is optional. If it is not provided, the length of the this value is used.

 Note 2

If start is negative, it is treated as length + start where length is the length of the array. If end is negative, it is treated as length + end.

This method performs the following steps when called:

  1. Let obj be ? ToObject(this value).
  2. Let length be ? LengthOfArrayLike(obj).
  3. Let k be ? ToClampedIndex(start, length).
  4. If end is undefined, let final be length; else let final be ? ToClampedIndex(end, length).
  5. Repeat, while k < final,
    1. Let propertyKey be ! ToString(𝔽(k)).
    2. Perform ? Set(obj, propertyKey, value, true).
    3. Set k to k + 1.
  6. Return obj.
 Note 3

This method is intentionally generic; it does not require that its this value be an Array. Therefore it can be transferred to other kinds of objects for use as a method.

23.1.3.8 Array.prototype.filter ( callback [ , thisArg ] )

Note 1

callback should be a function that accepts three arguments and returns a value that is coercible to a Boolean value. filter calls callback once for each element in the array, in ascending order, and constructs a new array of all the values for which callback returns true. callback is called only for elements of the array which actually exist; it is not called for missing elements of the array.

If a thisArg parameter is provided, it will be used as the this value for each invocation of callback. If it is not provided, undefined is used instead.

callback is called with three arguments: the value of the element, the index of the element, and the object being traversed.

filter does not directly mutate the object on which it is called but the object may be mutated by the calls to callback.

The range of elements processed by filter is set before the first call to callback. Elements which are appended to the array after the call to filter begins will not be visited by callback. If existing elements of the array are changed their value as passed to callback will be the value at the time filter visits them; elements that are deleted after the call to filter begins and before being visited are not visited.

This method performs the following steps when called:

  1. Let obj be ? ToObject(this value).
  2. Let length be ? LengthOfArrayLike(obj).
  3. If IsCallable(callback) is false, throw a TypeError exception.
  4. Let array be ? ArraySpeciesCreate(obj, 0).
  5. Let k be 0.
  6. Let to be 0.
  7. Repeat, while k < length,
    1. Let propertyKey be ! ToString(𝔽(k)).
    2. Let kPresent be ? HasProperty(obj, propertyKey).
    3. If kPresent is true, then
      1. Let kValue be ? Get(obj, propertyKey).
      2. Let selected be ToBoolean(? Call(callback, thisArg, « kValue, 𝔽(k), obj »)).
      3. If selected is true, then
        1. Perform ? CreateDataPropertyOrThrow(array, ! ToString(𝔽(to)), kValue).
        2. Set to to to + 1.
    4. Set k to k + 1.
  8. Return array.
 Note 2

This method is intentionally generic; it does not require that its this value be an Array. Therefore it can be transferred to other kinds of objects for use as a method.

23.1.3.9 Array.prototype.find ( predicate [ , thisArg ] )

Note 1

This method calls predicate once for each element of the array, in ascending index order, until it finds one where predicate returns a value that coerces to true. If such an element is found, find immediately returns that element value. Otherwise, find returns undefined.

See FindViaPredicate for additional information.

This method performs the following steps when called:

  1. Let obj be ? ToObject(this value).
  2. Let length be ? LengthOfArrayLike(obj).
  3. Let findRecord be ? FindViaPredicate(obj, length, ascending, predicate, thisArg).
  4. Return findRecord.[[Value]].
 Note 2

This method is intentionally generic; it does not require that its this value be an Array. Therefore it can be transferred to other kinds of objects for use as a method.

23.1.3.10 Array.prototype.findIndex ( predicate [ , thisArg ] )

Note 1

This method calls predicate once for each element of the array, in ascending index order, until it finds one where predicate returns a value that coerces to true. If such an element is found, findIndex immediately returns the index of that element value. Otherwise, findIndex returns -1.

See FindViaPredicate for additional information.

This method performs the following steps when called:

  1. Let obj be ? ToObject(this value).
  2. Let length be ? LengthOfArrayLike(obj).
  3. Let findRecord be ? FindViaPredicate(obj, length, ascending, predicate, thisArg).
  4. Return findRecord.[[Index]].
 Note 2

This method is intentionally generic; it does not require that its this value be an Array. Therefore it can be transferred to other kinds of objects for use as a method.

23.1.3.11 Array.prototype.findLast ( predicate [ , thisArg ] )

Note 1

This method calls predicate once for each element of the array, in descending index order, until it finds one where predicate returns a value that coerces to true. If such an element is found, findLast immediately returns that element value. Otherwise, findLast returns undefined.

See FindViaPredicate for additional information.

This method performs the following steps when called:

  1. Let obj be ? ToObject(this value).
  2. Let length be ? LengthOfArrayLike(obj).
  3. Let findRecord be ? FindViaPredicate(obj, length, descending, predicate, thisArg).
  4. Return findRecord.[[Value]].
 Note 2

This method is intentionally generic; it does not require that its this value be an Array object. Therefore it can be transferred to other kinds of objects for use as a method.

23.1.3.12 Array.prototype.findLastIndex ( predicate [ , thisArg ] )

Note 1

This method calls predicate once for each element of the array, in descending index order, until it finds one where predicate returns a value that coerces to true. If such an element is found, findLastIndex immediately returns the index of that element value. Otherwise, findLastIndex returns -1.

See FindViaPredicate for additional information.

This method performs the following steps when called:

  1. Let obj be ? ToObject(this value).
  2. Let length be ? LengthOfArrayLike(obj).
  3. Let findRecord be ? FindViaPredicate(obj, length, descending, predicate, thisArg).
  4. Return findRecord.[[Index]].
 Note 2

This method is intentionally generic; it does not require that its this value be an Array object. Therefore it can be transferred to other kinds of objects for use as a method.

23.1.3.12.1 FindViaPredicate ( obj, length, direction, predicate, thisArg )

The abstract operation FindViaPredicate takes arguments obj (an Object), length (a non-negative integer), direction (ascending or descending), predicate (an ECMAScript language value), and thisArg (an ECMAScript language value) and returns either a normal completion containing a Record with fields [[Index]] (an integral Number) and [[Value]] (an ECMAScript language value) or a throw completion.

obj should be an array-like object or a TypedArray. This operation calls predicate once for each element of obj, in either ascending index order or descending index order (as indicated by direction), until it finds one where predicate returns a value that coerces to true. At that point, this operation returns a Record that gives the index and value of the element found. If no such element is found, this operation returns a Record that specifies -1𝔽 for the index and undefined for the value.

predicate should be a function. When called for an element of the array, it is passed three arguments: the value of the element, the index of the element, and the object being traversed. Its return value will be coerced to a Boolean value.

thisArg will be used as the this value for each invocation of predicate.

This operation does not directly mutate the object on which it is called, but the object may be mutated by the calls to predicate.

The range of elements processed is set before the first call to predicate, just before the traversal begins. Elements that are appended to the array after this will not be visited by predicate. If existing elements of the array are changed, their value as passed to predicate will be the value at the time that this operation visits them. Elements that are deleted after traversal begins and before being visited are still visited and are either looked up from the prototype or are undefined.

It performs the following steps when called:

  1. If IsCallable(predicate) is false, throw a TypeError exception.
  2. If direction is ascending, then
    1. Let indices be a List of the integers in the interval from 0 (inclusive) to length (exclusive), in ascending order.
  3. Else,
    1. Let indices be a List of the integers in the interval from 0 (inclusive) to length (exclusive), in descending order.
  4. For each integer k of indices, do
    1. Let propertyKey be ! ToString(𝔽(k)).
    2. NOTE: If obj is a TypedArray, the following invocation of Get will return a normal completion.
    3. Let kValue be ? Get(obj, propertyKey).
    4. Let testResult be ? Call(predicate, thisArg, « kValue, 𝔽(k), obj »).
    5. If ToBoolean(testResult) is true, return the Record { [[Index]]: 𝔽(k), [[Value]]: kValue }.
  5. Return the Record { [[Index]]: -1𝔽, [[Value]]: undefined }.

23.1.3.13 Array.prototype.flat ( [ depth ] )

This method performs the following steps when called:

  1. Let obj be ? ToObject(this value).
  2. Let sourceLength be ? LengthOfArrayLike(obj).
  3. Let depthNumber be 1.
  4. If depth is not undefined, then
    1. Set depthNumber to ? ToIntegerOrInfinity(depth).
    2. If depthNumber < 0, set depthNumber to 0.
  5. Let array be ? ArraySpeciesCreate(obj, 0).
  6. Perform ? FlattenIntoArray(array, obj, sourceLength, 0, depthNumber).
  7. Return array.

23.1.3.13.1 FlattenIntoArray ( target, source, sourceLength, start, depth [ , mapperFunc [ , thisArg ] ] )

The abstract operation FlattenIntoArray takes arguments target (an Object), source (an Object), sourceLength (a non-negative integer), start (a non-negative integer), and depth (a non-negative integer or +∞) and optional arguments mapperFunc (a function object) and thisArg (an ECMAScript language value) and returns either a normal completion containing a non-negative integer or a throw completion. It performs the following steps when called:

  1. Assert: If mapperFunc is present, then IsCallable(mapperFunc) is true, thisArg is present, and depth is 1.
  2. Let targetIndex be start.
  3. Let sourceIndex be 0.
  4. Repeat, while sourceIndex < sourceLength,
    1. Let propertyKey be ! ToString(𝔽(sourceIndex)).
    2. Let exists be ? HasProperty(source, propertyKey).
    3. If exists is true, then
      1. Let element be ? Get(source, propertyKey).
      2. If mapperFunc is present, then
        1. Set element to ? Call(mapperFunc, thisArg, « element, 𝔽(sourceIndex), source »).
      3. Let shouldFlatten be false.
      4. If depth > 0, then
        1. Set shouldFlatten to ? IsArray(element).
      5. If shouldFlatten is true, then
        1. If depth = +∞, let newDepth be +∞.
        2. Else, let newDepth be depth - 1.
        3. Let elementLength be ? LengthOfArrayLike(element).
        4. Set targetIndex to ? FlattenIntoArray(target, element, elementLength, targetIndex, newDepth).
      6. Else,
        1. If targetIndex ≥ 253 - 1, throw a TypeError exception.
        2. Perform ? CreateDataPropertyOrThrow(target, ! ToString(𝔽(targetIndex)), element).
        3. Set targetIndex to targetIndex + 1.
    4. Set sourceIndex to sourceIndex + 1.
  5. Return targetIndex.

23.1.3.14 Array.prototype.flatMap ( mapperFunc [ , thisArg ] )

This method performs the following steps when called:

  1. Let obj be ? ToObject(this value).
  2. Let sourceLength be ? LengthOfArrayLike(obj).
  3. If IsCallable(mapperFunc) is false, throw a TypeError exception.
  4. Let array be ? ArraySpeciesCreate(obj, 0).
  5. Perform ? FlattenIntoArray(array, obj, sourceLength, 0, 1, mapperFunc, thisArg).
  6. Return array.

23.1.3.15 Array.prototype.forEach ( callback [ , thisArg ] )

Note 1

callback should be a function that accepts three arguments. forEach calls callback once for each element present in the array, in ascending order. callback is called only for elements of the array which actually exist; it is not called for missing elements of the array.

If a thisArg parameter is provided, it will be used as the this value for each invocation of callback. If it is not provided, undefined is used instead.

callback is called with three arguments: the value of the element, the index of the element, and the object being traversed.

forEach does not directly mutate the object on which it is called but the object may be mutated by the calls to callback.

The range of elements processed by forEach is set before the first call to callback. Elements which are appended to the array after the call to forEach begins will not be visited by callback. If existing elements of the array are changed, their value as passed to callback will be the value at the time forEach visits them; elements that are deleted after the call to forEach begins and before being visited are not visited.

This method performs the following steps when called:

  1. Let obj be ? ToObject(this value).
  2. Let length be ? LengthOfArrayLike(obj).
  3. If IsCallable(callback) is false, throw a TypeError exception.
  4. Let k be 0.
  5. Repeat, while k < length,
    1. Let propertyKey be ! ToString(𝔽(k)).
    2. Let kPresent be ? HasProperty(obj, propertyKey).
    3. If kPresent is true, then
      1. Let kValue be ? Get(obj, propertyKey).
      2. Perform ? Call(callback, thisArg, « kValue, 𝔽(k), obj »).
    4. Set k to k + 1.
  6. Return undefined.
 Note 2

This method is intentionally generic; it does not require that its this value be an Array. Therefore it can be transferred to other kinds of objects for use as a method.

23.1.3.16 Array.prototype.includes ( searchElement [ , fromIndex ] )

Note 1

This method compares searchElement to the elements of the array, in ascending order, using the SameValueZero algorithm, and if found at any position, returns true; otherwise, it returns false.

The optional second argument fromIndex defaults to +0𝔽 (i.e. the whole array is searched). If it is greater than or equal to the length of the array, false is returned, i.e. the array will not be searched. If it is less than -0𝔽, it is used as the offset from the end of the array to compute fromIndex. If the computed index is less than or equal to +0𝔽, the whole array will be searched.

This method performs the following steps when called:

  1. Let obj be ? ToObject(this value).
  2. Let length be ? LengthOfArrayLike(obj).
  3. If length = 0, return false.
  4. Let k be ? ToClampedIndex(fromIndex, length).
  5. Repeat, while k < length,
    1. Let elementK be ? Get(obj, ! ToString(𝔽(k))).
    2. If SameValueZero(searchElement, elementK) is true, return true.
    3. Set k to k + 1.
  6. Return false.
 Note 2

This method is intentionally generic; it does not require that its this value be an Array. Therefore it can be transferred to other kinds of objects for use as a method.

 Note 3

This method intentionally differs from the similar indexOf method in two ways. First, it uses the SameValueZero algorithm, instead of IsStrictlyEqual, allowing it to detect NaN array elements. Second, it does not skip missing array elements, instead treating them as undefined.

23.1.3.17 Array.prototype.indexOf ( searchElement [ , fromIndex ] )

This method compares searchElement to the elements of the array, in ascending order, using the IsStrictlyEqual algorithm, and if found at one or more indices, returns the smallest such index; otherwise, it returns -1𝔽.

Note 1

The optional second argument fromIndex defaults to +0𝔽 (i.e. the whole array is searched). If it is greater than or equal to the length of the array, -1𝔽 is returned, i.e. the array will not be searched. If it is less than -0𝔽, it is used to compute an offset from the end of the array. If the computed index is less than or equal to +0𝔽, the whole array will be searched.

This method performs the following steps when called:

  1. Let obj be ? ToObject(this value).
  2. Let length be ? LengthOfArrayLike(obj).
  3. If length = 0, return -1𝔽.
  4. Let k be ? ToClampedIndex(fromIndex, length).
  5. Repeat, while k < length,
    1. Let propertyKey be ! ToString(𝔽(k)).
    2. Let kPresent be ? HasProperty(obj, propertyKey).
    3. If kPresent is true, then
      1. Let elementK be ? Get(obj, propertyKey).
      2. If IsStrictlyEqual(searchElement, elementK) is true, return 𝔽(k).
    4. Set k to k + 1.
  6. Return -1𝔽.
 Note 2

This method is intentionally generic; it does not require that its this value be an Array. Therefore it can be transferred to other kinds of objects for use as a method.

23.1.3.18 Array.prototype.join ( separator )

This method converts the elements of the array to Strings, and then concatenates these Strings, separated by occurrences of the separator. If no separator is provided, a single comma is used as the separator.

It performs the following steps when called:

  1. Let obj be ? ToObject(this value).
  2. Let length be ? LengthOfArrayLike(obj).
  3. If separator is undefined, let separatorString be ","; else let separatorString be ? ToString(separator).
  4. Return ? JoinIndexedProperties(obj, length, separatorString).
 Note

This method is intentionally generic; it does not require that its this value be an Array. Therefore, it can be transferred to other kinds of objects for use as a method.

23.1.3.18.1 JoinIndexedProperties ( obj, length, separator [ , methodName [ , methodArgs ] ] )

The abstract operation JoinIndexedProperties takes arguments obj (an Object), length (a non-negative integer), and separator (a String) and optional arguments methodName (a property key) and methodArgs (a List of ECMAScript language values) and returns either a normal completion containing a String or a throw completion. It converts the integer index properties of obj in the inclusive interval from 0 to length - 1 to Strings (optionally via method invocation), and then concatenates those Strings, separated by occurrences of a separator String. It performs the following steps when called:

  1. If methodName is present and methodArgs is not present, set methodArgs to a new empty List.
  2. Let result be the empty String.
  3. Let k be 0.
  4. Repeat, while k < length,
    1. If k > 0, set result to the string-concatenation of result and separator.
    2. NOTE: If obj is a TypedArray, the following invocation of Get will return a normal completion.
    3. Let element be ? Get(obj, ! ToString(𝔽(k))).
    4. If element is neither undefined nor null, then
      1. If methodName is present, then
        1. Let elementString be ? ToString(? Invoke(element, methodName, methodArgs)).
      2. Else,
        1. NOTE: If obj is a TypedArray, the following invocation of ToString will return a normal completion.
        2. Let elementString be ? ToString(element).
      3. Set result to the string-concatenation of result and elementString.
    5. Set k to k + 1.
  5. Return result.
 Note

The methodArgs parameter is intended for use by other specifications that rely upon this operation, such as ECMA-402.

23.1.3.19 Array.prototype.keys ( )

This method performs the following steps when called:

  1. Let obj be ? ToObject(this value).
  2. Return CreateArrayIterator(obj, key).

23.1.3.20 Array.prototype.lastIndexOf ( searchElement [ , fromIndex ] )

Note 1

This method compares searchElement to the elements of the array in descending order using the IsStrictlyEqual algorithm, and if found at one or more indices, returns the largest such index; otherwise, it returns -1𝔽.

The optional second argument fromIndex defaults to the array's length minus one (i.e. the whole array is searched). If it is greater than or equal to the length of the array, the whole array will be searched. If it is less than -0𝔽, it is used to compute an offset from the end of the array. If the computed index is less than -0𝔽, -1𝔽 is returned.

This method performs the following steps when called:

  1. Let obj be ? ToObject(this value).
  2. Let length be ? LengthOfArrayLike(obj).
  3. If length = 0, return -1𝔽.
  4. If fromIndex is not present, let k be length - 1; else let k be min(? ToAbsoluteIndex(fromIndex, length), length - 1).
  5. Repeat, while k ≥ 0,
    1. Let propertyKey be ! ToString(𝔽(k)).
    2. Let kPresent be ? HasProperty(obj, propertyKey).
    3. If kPresent is true, then
      1. Let elementK be ? Get(obj, propertyKey).
      2. If IsStrictlyEqual(searchElement, elementK) is true, return 𝔽(k).
    4. Set k to k - 1.
  6. Return -1𝔽.
 Note 2

This method is intentionally generic; it does not require that its this value be an Array. Therefore it can be transferred to other kinds of objects for use as a method.

23.1.3.21 Array.prototype.map ( callback [ , thisArg ] )

Note 1

callback should be a function that accepts three arguments. map calls callback once for each element in the array, in ascending order, and constructs a new Array from the results. callback is called only for elements of the array which actually exist; it is not called for missing elements of the array.

If a thisArg parameter is provided, it will be used as the this value for each invocation of callback. If it is not provided, undefined is used instead.

callback is called with three arguments: the value of the element, the index of the element, and the object being traversed.

map does not directly mutate the object on which it is called but the object may be mutated by the calls to callback.

The range of elements processed by map is set before the first call to callback. Elements which are appended to the array after the call to map begins will not be visited by callback. If existing elements of the array are changed, their value as passed to callback will be the value at the time map visits them; elements that are deleted after the call to map begins and before being visited are not visited.

This method performs the following steps when called:

  1. Let obj be ? ToObject(this value).
  2. Let length be ? LengthOfArrayLike(obj).
  3. If IsCallable(callback) is false, throw a TypeError exception.
  4. Let array be ? ArraySpeciesCreate(obj, length).
  5. Let k be 0.
  6. Repeat, while k < length,
    1. Let propertyKey be ! ToString(𝔽(k)).
    2. Let kPresent be ? HasProperty(obj, propertyKey).
    3. If kPresent is true, then
      1. Let kValue be ? Get(obj, propertyKey).
      2. Let mappedValue be ? Call(callback, thisArg, « kValue, 𝔽(k), obj »).
      3. Perform ? CreateDataPropertyOrThrow(array, propertyKey, mappedValue).
    4. Set k to k + 1.
  7. Return array.
 Note 2

This method is intentionally generic; it does not require that its this value be an Array. Therefore it can be transferred to other kinds of objects for use as a method.

23.1.3.22 Array.prototype.pop ( )

Note 1

This method removes the last element of the array and returns it.

This method performs the following steps when called:

  1. Let obj be ? ToObject(this value).
  2. Let length be ? LengthOfArrayLike(obj).
  3. If length = 0, then
    1. Perform ? Set(obj, "length", +0𝔽, true).
    2. Return undefined.
  4. Assert: length > 0.
  5. Let newLength be 𝔽(length - 1).
  6. Let index be ! ToString(newLength).
  7. Let element be ? Get(obj, index).
  8. Perform ? DeletePropertyOrThrow(obj, index).
  9. Perform ? Set(obj, "length", newLength, true).
  10. Return element.
 Note 2

This method is intentionally generic; it does not require that its this value be an Array. Therefore it can be transferred to other kinds of objects for use as a method.

23.1.3.23 Array.prototype.push ( ...items )

Note 1

This method appends the arguments to the end of the array, in the order in which they appear. It returns the new length of the array.

This method performs the following steps when called:

  1. Let obj be ? ToObject(this value).
  2. Let length be ? LengthOfArrayLike(obj).
  3. Let argCount be the number of elements in items.
  4. If length + argCount > 253 - 1, throw a TypeError exception.
  5. For each element item of items, do
    1. Perform ? Set(obj, ! ToString(𝔽(length)), item, true).
    2. Set length to length + 1.
  6. Perform ? Set(obj, "length", 𝔽(length), true).
  7. Return 𝔽(length).

The "length" property of this method is 1𝔽.

Note 2

This method is intentionally generic; it does not require that its this value be an Array. Therefore it can be transferred to other kinds of objects for use as a method.

23.1.3.24 Array.prototype.reduce ( callback [ , initialValue ] )

Note 1

callback should be a function that takes four arguments. reduce calls callback once for each element present in the array, in ascending order, skipping the first element unless initialValue is provided.

callback is called with four arguments: the previousValue (value from the previous call to callback), the currentValue (value of the current element), the currentIndex, and the object being traversed. The first time that callback is called, the previousValue and currentValue can be one of two values. If an initialValue was supplied in the call to reduce, then previousValue will be initialValue and currentValue will be the first value in the array. If no initialValue was supplied, then previousValue will be the first value in the array and currentValue will be the second. It is a TypeError if the array contains no elements and initialValue is not provided.

reduce does not directly mutate the object on which it is called but the object may be mutated by the calls to callback.

The range of elements processed by reduce is set before the first call to callback. Elements that are appended to the array after the call to reduce begins will not be visited by callback. If existing elements of the array are changed, their value as passed to callback will be the value at the time reduce visits them; elements that are deleted after the call to reduce begins and before being visited are not visited.

This method performs the following steps when called:

  1. Let obj be ? ToObject(this value).
  2. Let length be ? LengthOfArrayLike(obj).
  3. If IsCallable(callback) is false, throw a TypeError exception.
  4. If length = 0 and initialValue is not present, throw a TypeError exception.
  5. Let k be 0.
  6. Let accumulator be undefined.
  7. If initialValue is present, then
    1. Set accumulator to initialValue.
  8. Else,
    1. Let kPresent be false.
    2. Repeat, while kPresent is false and k < length,
      1. Let propertyKey be ! ToString(𝔽(k)).
      2. Set kPresent to ? HasProperty(obj, propertyKey).
      3. If kPresent is true, then
        1. Set accumulator to ? Get(obj, propertyKey).
      4. Set k to k + 1.
    3. If kPresent is false, throw a TypeError exception.
  9. Repeat, while k < length,
    1. Let propertyKey be ! ToString(𝔽(k)).
    2. Let kPresent be ? HasProperty(obj, propertyKey).
    3. If kPresent is true, then
      1. Let kValue be ? Get(obj, propertyKey).
      2. Set accumulator to ? Call(callback, undefined, « accumulator, kValue, 𝔽(k), obj »).
    4. Set k to k + 1.
  10. Return accumulator.
 Note 2

This method is intentionally generic; it does not require that its this value be an Array. Therefore it can be transferred to other kinds of objects for use as a method.

23.1.3.25 Array.prototype.reduceRight ( callback [ , initialValue ] )

Note 1

callback should be a function that takes four arguments. reduceRight calls callback once for each element present in the array, in descending order, skipping the first call unless initialValue is provided.

callback is called with four arguments: the previousValue (value from the previous call to callback), the currentValue (value of the current element), the currentIndex, and the object being traversed. The first time the function is called, the previousValue and currentValue can be one of two values. If an initialValue was supplied in the call to reduceRight, then previousValue will be initialValue and currentValue will be the last value in the array. If no initialValue was supplied, then previousValue will be the last value in the array and currentValue will be the second-to-last value. It is a TypeError if the array contains no elements and initialValue is not provided.

reduceRight does not directly mutate the object on which it is called but the object may be mutated by the calls to callback.

The range of elements processed by reduceRight is set before the first call to callback. Elements that are appended to the array after the call to reduceRight begins will not be visited by callback. If existing elements of the array are changed by callback, their value as passed to callback will be the value at the time reduceRight visits them; elements that are deleted after the call to reduceRight begins and before being visited are not visited.

This method performs the following steps when called:

  1. Let obj be ? ToObject(this value).
  2. Let length be ? LengthOfArrayLike(obj).
  3. If IsCallable(callback) is false, throw a TypeError exception.
  4. If length = 0 and initialValue is not present, throw a TypeError exception.
  5. Let k be length - 1.
  6. Let accumulator be undefined.
  7. If initialValue is present, then
    1. Set accumulator to initialValue.
  8. Else,
    1. Let kPresent be false.
    2. Repeat, while kPresent is false and k ≥ 0,
      1. Let propertyKey be ! ToString(𝔽(k)).
      2. Set kPresent to ? HasProperty(obj, propertyKey).
      3. If kPresent is true, then
        1. Set accumulator to ? Get(obj, propertyKey).
      4. Set k to k - 1.
    3. If kPresent is false, throw a TypeError exception.
  9. Repeat, while k ≥ 0,
    1. Let propertyKey be ! ToString(𝔽(k)).
    2. Let kPresent be ? HasProperty(obj, propertyKey).
    3. If kPresent is true, then
      1. Let kValue be ? Get(obj, propertyKey).
      2. Set accumulator to ? Call(callback, undefined, « accumulator, kValue, 𝔽(k), obj »).
    4. Set k to k - 1.
  10. Return accumulator.
 Note 2

This method is intentionally generic; it does not require that its this value be an Array. Therefore it can be transferred to other kinds of objects for use as a method.

23.1.3.26 Array.prototype.reverse ( )

Note 1

This method rearranges the elements of the array so as to reverse their order. It returns the reversed array.

This method performs the following steps when called:

  1. Let obj be ? ToObject(this value).
  2. Let length be ? LengthOfArrayLike(obj).
  3. Let middle be floor(length / 2).
  4. Let lower be 0.
  5. Repeat, while lower ≠ middle,
    1. Let upper be length - lower - 1.
    2. Let upperP be ! ToString(𝔽(upper)).
    3. Let lowerP be ! ToString(𝔽(lower)).
    4. Let lowerExists be ? HasProperty(obj, lowerP).
    5. If lowerExists is true, then
      1. Let lowerValue be ? Get(obj, lowerP).
    6. Let upperExists be ? HasProperty(obj, upperP).
    7. If upperExists is true, then
      1. Let upperValue be ? Get(obj, upperP).
    8. If lowerExists is true and upperExists is true, then
      1. Perform ? Set(obj, lowerP, upperValue, true).
      2. Perform ? Set(obj, upperP, lowerValue, true).
    9. Else if lowerExists is false and upperExists is true, then
      1. Perform ? Set(obj, lowerP, upperValue, true).
      2. Perform ? DeletePropertyOrThrow(obj, upperP).
    10. Else if lowerExists is true and upperExists is false, then
      1. Perform ? DeletePropertyOrThrow(obj, lowerP).
      2. Perform ? Set(obj, upperP, lowerValue, true).
    11. Else,
      1. Assert: lowerExists and upperExists are both false.
      2. NOTE: No action is required.
    12. Set lower to lower + 1.
  6. Return obj.
 Note 2

This method is intentionally generic; it does not require that its this value be an Array. Therefore, it can be transferred to other kinds of objects for use as a method.

23.1.3.27 Array.prototype.shift ( )

This method removes the first element of the array and returns it.

It performs the following steps when called:

  1. Let obj be ? ToObject(this value).
  2. Let length be ? LengthOfArrayLike(obj).
  3. If length = 0, then
    1. Perform ? Set(obj, "length", +0𝔽, true).
    2. Return undefined.
  4. Let first be ? Get(obj, "0").
  5. Let k be 1.
  6. Repeat, while k < length,
    1. Let from be ! ToString(𝔽(k)).
    2. Let to be ! ToString(𝔽(k - 1)).
    3. Let fromPresent be ? HasProperty(obj, from).
    4. If fromPresent is true, then
      1. Let fromValue be ? Get(obj, from).
      2. Perform ? Set(obj, to, fromValue, true).
    5. Else,
      1. Assert: fromPresent is false.
      2. Perform ? DeletePropertyOrThrow(obj, to).
    6. Set k to k + 1.
  7. Perform ? DeletePropertyOrThrow(obj, ! ToString(𝔽(length - 1))).
  8. Perform ? Set(obj, "length", 𝔽(length - 1), true).
  9. Return first.
 Note

This method is intentionally generic; it does not require that its this value be an Array. Therefore it can be transferred to other kinds of objects for use as a method.

23.1.3.28 Array.prototype.slice ( start, end )

This method returns an array containing the elements of the array from element start up to, but not including, element end (or through the end of the array if end is undefined). If start is negative, it is treated as length + start where length is the length of the array. If end is negative, it is treated as length + end where length is the length of the array.

It performs the following steps when called:

  1. Let obj be ? ToObject(this value).
  2. Let length be ? LengthOfArrayLike(obj).
  3. Let k be ? ToClampedIndex(start, length).
  4. If end is undefined, let final be length; else let final be ? ToClampedIndex(end, length).
  5. Let count be max(final - k, 0).
  6. Let array be ? ArraySpeciesCreate(obj, count).
  7. Let resultIndex be 0.
  8. Repeat, while k < final,
    1. Let propertyKey be ! ToString(𝔽(k)).
    2. Let kPresent be ? HasProperty(obj, propertyKey).
    3. If kPresent is true, then
      1. Let kValue be ? Get(obj, propertyKey).
      2. Perform ? CreateDataPropertyOrThrow(array, ! ToString(𝔽(resultIndex)), kValue).
    4. Set k to k + 1.
    5. Set resultIndex to resultIndex + 1.
  9. Perform ? Set(array, "length", 𝔽(resultIndex), true).
  10. Return array.
 Note 1

The explicit setting of the "length" property in step 9 is intended to ensure the length is correct even when array is not a built-in Array.

 Note 2

This method is intentionally generic; it does not require that its this value be an Array. Therefore it can be transferred to other kinds of objects for use as a method.

23.1.3.29 Array.prototype.some ( callback [ , thisArg ] )

Note 1

callback should be a function that accepts three arguments and returns a value that is coercible to a Boolean value. some calls callback once for each element present in the array, in ascending order, until it finds one where callback returns true. If such an element is found, some immediately returns true. Otherwise, some returns false. callback is called only for elements of the array which actually exist; it is not called for missing elements of the array.

If a thisArg parameter is provided, it will be used as the this value for each invocation of callback. If it is not provided, undefined is used instead.

callback is called with three arguments: the value of the element, the index of the element, and the object being traversed.

some does not directly mutate the object on which it is called but the object may be mutated by the calls to callback.

The range of elements processed by some is set before the first call to callback. Elements that are appended to the array after the call to some begins will not be visited by callback. If existing elements of the array are changed, their value as passed to callback will be the value at the time that some visits them; elements that are deleted after the call to some begins and before being visited are not visited. some acts like the “exists” quantifier in mathematics. In particular, for an empty array, it returns false.

This method performs the following steps when called:

  1. Let obj be ? ToObject(this value).
  2. Let length be ? LengthOfArrayLike(obj).
  3. If IsCallable(callback) is false, throw a TypeError exception.
  4. Let k be 0.
  5. Repeat, while k < length,
    1. Let propertyKey be ! ToString(𝔽(k)).
    2. Let kPresent be ? HasProperty(obj, propertyKey).
    3. If kPresent is true, then
      1. Let kValue be ? Get(obj, propertyKey).
      2. Let testResult be ToBoolean(? Call(callback, thisArg, « kValue, 𝔽(k), obj »)).
      3. If testResult is true, return true.
    4. Set k to k + 1.
  6. Return false.
 Note 2

This method is intentionally generic; it does not require that its this value be an Array. Therefore it can be transferred to other kinds of objects for use as a method.

23.1.3.30 Array.prototype.sort ( comparator )

This method sorts the elements of this array. If comparator is not undefined, it should be a function that accepts two arguments x and y and returns a negative Number if x < y, a positive Number if x > y, or a zero otherwise.

It performs the following steps when called:

  1. If comparator is not undefined and IsCallable(comparator) is false, throw a TypeError exception.
  2. Let obj be ? ToObject(this value).
  3. Let length be ? LengthOfArrayLike(obj).
  4. Let sortCompare be a new Abstract Closure with parameters (x, y) that captures comparator and performs the following steps when called:
    1. Return ? CompareArrayElements(x, y, comparator).
  5. Let sortedList be ? SortIndexedProperties(obj, length, sortCompare, skip-holes).
  6. Let itemCount be the number of elements in sortedList.
  7. Let j be 0.
  8. Repeat, while j < itemCount,
    1. Perform ? Set(obj, ! ToString(𝔽(j)), sortedList[j], true).
    2. Set j to j + 1.
  9. NOTE: The call to SortIndexedProperties in step 5 uses skip-holes. The remaining indices are deleted to preserve the number of holes that were detected and excluded from the sort.
  10. Repeat, while j < length,
    1. Perform ? DeletePropertyOrThrow(obj, ! ToString(𝔽(j))).
    2. Set j to j + 1.
  11. Return obj.
 Note 1

Because non-existent property values always compare greater than undefined property values, and undefined always compares greater than any other value (see CompareArrayElements), undefined property values always sort to the end of the result, followed by non-existent property values.

 Note 2

Method calls performed by the ToString abstract operations in steps 5 and 6 have the potential to cause sortCompare to not behave as a consistent comparator.

 Note 3

This method is intentionally generic; it does not require that its this value be an Array. Therefore, it can be transferred to other kinds of objects for use as a method.

23.1.3.30.1 SortIndexedProperties ( obj, length, sortCompare, holes )

The abstract operation SortIndexedProperties takes arguments obj (an Object), length (a non-negative integer), sortCompare (an Abstract Closure with two parameters), and holes (skip-holes or read-through-holes) and returns either a normal completion containing a List of ECMAScript language values or a throw completion. It performs the following steps when called:

  1. Let items be a new empty List.
  2. Let k be 0.
  3. Repeat, while k < length,
    1. Let propertyKey be ! ToString(𝔽(k)).
    2. If holes is skip-holes, then
      1. Let kRead be ? HasProperty(obj, propertyKey).
    3. Else,
      1. Assert: holes is read-through-holes.
      2. Let kRead be true.
    4. If kRead is true, then
      1. Let kValue be ? Get(obj, propertyKey).
      2. Append kValue to items.
    5. Set k to k + 1.
  4. Sort items using an implementation-defined sequence of calls to sortCompare. If any such call returns an abrupt completion, stop before performing any further calls to sortCompare and return that Completion Record.
  5. Return items.

The sort order is the ordering of items after completion of step 4 of the algorithm above. The sort order is implementation-defined if sortCompare is not a consistent comparator for the elements of items. When SortIndexedProperties is invoked by Array.prototype.sort or Array.prototype.toSorted, the sort order is also implementation-defined if comparator is undefined, and all applications of ToString, to any specific value passed as an argument to sortCompare, do not produce the same result.

Unless the sort order is specified to be implementation-defined, it must satisfy all of the following conditions:

  • There must be some mathematical permutation π of the non-negative integers less than itemCount, such that for every non-negative integer j less than itemCount, the element old[j] is exactly the same as new[π(j)].
  • Then for all non-negative integers j and k, each less than itemCount, if ℝ(sortCompare(old[j], old[k])) < 0, then π(j) < π(k).
  • And for all non-negative integers j and k such that j < k < itemCount, if ℝ(sortCompare(old[j], old[k])) = 0, then π(j) < π(k); i.e., the sort is stable.

Here the notation old[j] is used to refer to items[j] before step 4 is executed, and the notation new[j] to refer to items[j] after step 4 has been executed.

An Abstract Closure or function comparator is a consistent comparator for a set of values values if all of the requirements below are met for all values a, b, and c (possibly the same value) in the set values: The notation a <C b means ℝ(comparator(a, b)) < 0; a =C b means ℝ(comparator(a, b)) = 0; and a >C b means ℝ(comparator(a, b)) > 0.

  • Calling comparator(a, b) always returns the same value v when given a specific pair of values a and b as its two arguments. Furthermore, v is a Number, and v is not NaN. Note that this implies that exactly one of a <C b, a =C b, and a >C b will be true for a given pair of a and b.
  • Calling comparator(a, b) does not modify obj or any object on obj's prototype chain.
  • a =C a (reflexivity)
  • If a =C b, then b =C a (symmetry)
  • If a =C b and b =C c, then a =C c (transitivity of =C)
  • If a <C b and b <C c, then a <C c (transitivity of <C)
  • If a >C b and b >C c, then a >C c (transitivity of >C)
Note

The above conditions are necessary and sufficient to ensure that comparator divides the set values into equivalence classes and that these equivalence classes are totally ordered.

23.1.3.30.2 CompareArrayElements ( x, y, comparator )

The abstract operation CompareArrayElements takes arguments x (an ECMAScript language value), y (an ECMAScript language value), and comparator (a function object or undefined) and returns either a normal completion containing a Number or an abrupt completion. It performs the following steps when called:

  1. If x is undefined and y is undefined, return +0𝔽.
  2. If x is undefined, return 1𝔽.
  3. If y is undefined, return -1𝔽.
  4. If comparator is not undefined, then
    1. Let result be ? ToNumber(? Call(comparator, undefined, « x, y »)).
    2. If result is NaN, return +0𝔽.
    3. Return result.
  5. Let xString be ? ToString(x).
  6. Let yString be ? ToString(y).
  7. Let xSmaller be ! IsLessThan(xString, yString, true).
  8. If xSmaller is true, return -1𝔽.
  9. Let ySmaller be ! IsLessThan(yString, xString, true).
  10. If ySmaller is true, return 1𝔽.
  11. Return +0𝔽.

23.1.3.31 Array.prototype.splice ( start, deleteCount, ...items )

Note 1

This method deletes the deleteCount elements of the array starting at integer index start and replaces them with the elements of items. It returns an Array containing the deleted elements (if any).

This method performs the following steps when called:

  1. Let obj be ? ToObject(this value).
  2. Let length be ? LengthOfArrayLike(obj).
  3. Let actualStart be ? ToClampedIndex(start, length).
  4. Let itemCount be the number of elements in items.
  5. If start is not present, then
    1. Let actualDeleteCount be 0.
  6. Else if deleteCount is not present, then
    1. Let actualDeleteCount be length - actualStart.
    2. Assert: actualDeleteCount ≥ 0.
  7. Else,
    1. Let dc be ? ToIntegerOrInfinity(deleteCount).
    2. Let actualDeleteCount be the result of clamping dc between 0 and length - actualStart.
  8. If length + itemCount - actualDeleteCount > 253 - 1, throw a TypeError exception.
  9. Let deletedArray be ? ArraySpeciesCreate(obj, actualDeleteCount).
  10. Let k be 0.
  11. Repeat, while k < actualDeleteCount,
    1. Let from be ! ToString(𝔽(actualStart + k)).
    2. If ? HasProperty(obj, from) is true, then
      1. Let fromValue be ? Get(obj, from).
      2. Perform ? CreateDataPropertyOrThrow(deletedArray, ! ToString(𝔽(k)), fromValue).
    3. Set k to k + 1.
  12. Perform ? Set(deletedArray, "length", 𝔽(actualDeleteCount), true).
  13. If itemCount < actualDeleteCount, then
    1. Set k to actualStart.
    2. Repeat, while k < (length - actualDeleteCount),
      1. Let from be ! ToString(𝔽(k + actualDeleteCount)).
      2. Let to be ! ToString(𝔽(k + itemCount)).
      3. If ? HasProperty(obj, from) is true, then
        1. Let fromValue be ? Get(obj, from).
        2. Perform ? Set(obj, to, fromValue, true).
      4. Else,
        1. Perform ? DeletePropertyOrThrow(obj, to).
      5. Set k to k + 1.
    3. Set k to length.
    4. Repeat, while k > (length - actualDeleteCount + itemCount),
      1. Perform ? DeletePropertyOrThrow(obj, ! ToString(𝔽(k - 1))).
      2. Set k to k - 1.
  14. Else if itemCount > actualDeleteCount, then
    1. Set k to (length - actualDeleteCount).
    2. Repeat, while k > actualStart,
      1. Let from be ! ToString(𝔽(k + actualDeleteCount - 1)).
      2. Let to be ! ToString(𝔽(k + itemCount - 1)).
      3. If ? HasProperty(obj, from) is true, then
        1. Let fromValue be ? Get(obj, from).
        2. Perform ? Set(obj, to, fromValue, true).
      4. Else,
        1. Perform ? DeletePropertyOrThrow(obj, to).
      5. Set k to k - 1.
  15. Set k to actualStart.
  16. For each element item of items, do
    1. Perform ? Set(obj, ! ToString(𝔽(k)), item, true).
    2. Set k to k + 1.
  17. Perform ? Set(obj, "length", 𝔽(length - actualDeleteCount + itemCount), true).
  18. Return deletedArray.
 Note 2

The explicit setting of the "length" property in steps 12 and 17 is intended to ensure the lengths are correct even when the objects are not built-in Arrays.

 Note 3

This method is intentionally generic; it does not require that its this value be an Array. Therefore it can be transferred to other kinds of objects for use as a method.

23.1.3.32 Array.prototype.toLocaleString ( [ reserved1 [ , reserved2 ] ] )

An ECMAScript implementation that includes the ECMA-402 Internationalization API must implement this method as specified in ECMA-402. Otherwise, the following specification of this method is used.

Note 1

The first edition of ECMA-402 did not include a replacement specification for this method.

The meanings of the optional parameters to this method are defined in ECMA-402; implementations that do not include ECMA-402 support must not use those parameter positions for anything else.

This method performs the following steps when called:

  1. Let array be ? ToObject(this value).
  2. Let length be ? LengthOfArrayLike(array).
  3. Return ? JoinIndexedProperties(array, length, LocalizedListSeparator(), "toLocaleString").
 Note 2

This method is analogous to toString except that it is intended to yield a locale-sensitive result corresponding with conventions of the host environment's current locale.

 Note 3

This method is intentionally generic; it does not require that its this value be an Array. Therefore it can be transferred to other kinds of objects for use as a method.

23.1.3.32.1 LocalizedListSeparator ( )

The implementation-defined abstract operation LocalizedListSeparator takes no arguments and returns a String. It returns an implementation-defined String appropriate for use as a list separator in the host environment's current locale (such as ", ").

23.1.3.33 Array.prototype.toReversed ( )

This method performs the following steps when called:

  1. Let obj be ? ToObject(this value).
  2. Let length be ? LengthOfArrayLike(obj).
  3. Let array be ? ArrayCreate(length).
  4. Let k be 0.
  5. Repeat, while k < length,
    1. Let from be ! ToString(𝔽(length - k - 1)).
    2. Let propertyKey be ! ToString(𝔽(k)).
    3. Let fromValue be ? Get(obj, from).
    4. Perform ! CreateDataPropertyOrThrow(array, propertyKey, fromValue).
    5. Set k to k + 1.
  6. Return array.

23.1.3.34 Array.prototype.toSorted ( comparator )

This method performs the following steps when called:

  1. If comparator is not undefined and IsCallable(comparator) is false, throw a TypeError exception.
  2. Let obj be ? ToObject(this value).
  3. Let length be ? LengthOfArrayLike(obj).
  4. Let array be ? ArrayCreate(length).
  5. Let sortCompare be a new Abstract Closure with parameters (x, y) that captures comparator and performs the following steps when called:
    1. Return ? CompareArrayElements(x, y, comparator).
  6. Let sortedList be ? SortIndexedProperties(obj, length, sortCompare, read-through-holes).
  7. Let j be 0.
  8. Repeat, while j < length,
    1. Perform ! CreateDataPropertyOrThrow(array, ! ToString(𝔽(j)), sortedList[j]).
    2. Set j to j + 1.
  9. Return array.

23.1.3.35 Array.prototype.toSpliced ( start, skipCount, ...items )

This method performs the following steps when called:

  1. Let obj be ? ToObject(this value).
  2. Let length be ? LengthOfArrayLike(obj).
  3. Let actualStart be ? ToClampedIndex(start, length).
  4. Let insertCount be the number of elements in items.
  5. Let maxSkipCount be length - actualStart.
  6. If start is not present, then
    1. Let actualSkipCount be 0.
  7. Else if skipCount is not present, then
    1. Let actualSkipCount be maxSkipCount.
  8. Else,
    1. Let actualSkipCount be the result of clamping ? ToIntegerOrInfinity(skipCount) between 0 and maxSkipCount.
  9. Let newLength be length + insertCount - actualSkipCount.
  10. Assert: newLength ≥ 0.
  11. If newLength > 253 - 1, throw a TypeError exception.
  12. Let newArray be ? ArrayCreate(newLength).
  13. Let writeIndex be 0.
  14. Let readIndex be actualStart + actualSkipCount.
  15. Repeat, while writeIndex < actualStart,
    1. Let propertyKey be ! ToString(𝔽(writeIndex)).
    2. Let iValue be ? Get(obj, propertyKey).
    3. Perform ! CreateDataPropertyOrThrow(newArray, propertyKey, iValue).
    4. Set writeIndex to writeIndex + 1.
  16. For each element item of items, do
    1. Let propertyKey be ! ToString(𝔽(writeIndex)).
    2. Perform ! CreateDataPropertyOrThrow(newArray, propertyKey, item).
    3. Set writeIndex to writeIndex + 1.
  17. Repeat, while writeIndex < newLength,
    1. Let propertyKey be ! ToString(𝔽(writeIndex)).
    2. Let from be ! ToString(𝔽(readIndex)).
    3. Let fromValue be ? Get(obj, from).
    4. Perform ! CreateDataPropertyOrThrow(newArray, propertyKey, fromValue).
    5. Set writeIndex to writeIndex + 1.
    6. Set readIndex to readIndex + 1.
  18. Return newArray.

23.1.3.36 Array.prototype.toString ( )

This method performs the following steps when called:

  1. Let array be ? ToObject(this value).
  2. Let func be ? Get(array, "join").
  3. If IsCallable(func) is false, set func to the intrinsic function %Object.prototype.toString%.
  4. Return ? Call(func, array).
 Note

This method is intentionally generic; it does not require that its this value be an Array. Therefore it can be transferred to other kinds of objects for use as a method.

23.1.3.37 Array.prototype.unshift ( ...items )

This method prepends the arguments to the start of the array, such that their order within the array is the same as the order in which they appear in the argument list.

It performs the following steps when called:

  1. Let obj be ? ToObject(this value).
  2. Let length be ? LengthOfArrayLike(obj).
  3. Let argCount be the number of elements in items.
  4. If argCount > 0, then
    1. If length + argCount > 253 - 1, throw a TypeError exception.
    2. Let k be length.
    3. Repeat, while k > 0,
      1. Let from be ! ToString(𝔽(k - 1)).
      2. Let to be ! ToString(𝔽(k + argCount - 1)).
      3. Let fromPresent be ? HasProperty(obj, from).
      4. If fromPresent is true, then
        1. Let fromValue be ? Get(obj, from).
        2. Perform ? Set(obj, to, fromValue, true).
      5. Else,
        1. Assert: fromPresent is false.
        2. Perform ? DeletePropertyOrThrow(obj, to).
      6. Set k to k - 1.
    4. Let j be 0.
    5. For each element item of items, do
      1. Perform ? Set(obj, ! ToString(𝔽(j)), item, true).
      2. Set j to j + 1.
  5. Perform ? Set(obj, "length", 𝔽(length + argCount), true).
  6. Return 𝔽(length + argCount).

The "length" property of this method is 1𝔽.

Note

This method is intentionally generic; it does not require that its this value be an Array. Therefore it can be transferred to other kinds of objects for use as a method.

23.1.3.38 Array.prototype.values ( )

This method performs the following steps when called:

  1. Let obj be ? ToObject(this value).
  2. Return CreateArrayIterator(obj, value).

23.1.3.39 Array.prototype.with ( index, value )

This method performs the following steps when called:

  1. Let obj be ? ToObject(this value).
  2. Let length be ? LengthOfArrayLike(obj).
  3. Let actualIndex be ? ToAbsoluteIndex(index, length).
  4. If actualIndex < 0 or actualIndex ≥ length, throw a RangeError exception.
  5. Let array be ? ArrayCreate(length).
  6. Let k be 0.
  7. Repeat, while k < length,
    1. Let propertyKey be ! ToString(𝔽(k)).
    2. If k = actualIndex, let fromValue be value.
    3. Else, let fromValue be ? Get(obj, propertyKey).
    4. Perform ! CreateDataPropertyOrThrow(array, propertyKey, fromValue).
    5. Set k to k + 1.
  8. Return array.

23.1.3.40 Array.prototype [ %Symbol.iterator% ] ( )

The initial value of the %Symbol.iterator% property is %Array.prototype.values%, defined in 23.1.3.38.

23.1.3.41 Array.prototype [ %Symbol.unscopables% ]

The initial value of the %Symbol.unscopables% data property is an object created by the following steps:

  1. Let unscopableList be OrdinaryObjectCreate(null).
  2. Perform ! CreateDataPropertyOrThrow(unscopableList, "at", true).
  3. Perform ! CreateDataPropertyOrThrow(unscopableList, "copyWithin", true).
  4. Perform ! CreateDataPropertyOrThrow(unscopableList, "entries", true).
  5. Perform ! CreateDataPropertyOrThrow(unscopableList, "fill", true).
  6. Perform ! CreateDataPropertyOrThrow(unscopableList, "find", true).
  7. Perform ! CreateDataPropertyOrThrow(unscopableList, "findIndex", true).
  8. Perform ! CreateDataPropertyOrThrow(unscopableList, "findLast", true).
  9. Perform ! CreateDataPropertyOrThrow(unscopableList, "findLastIndex", true).
  10. Perform ! CreateDataPropertyOrThrow(unscopableList, "flat", true).
  11. Perform ! CreateDataPropertyOrThrow(unscopableList, "flatMap", true).
  12. Perform ! CreateDataPropertyOrThrow(unscopableList, "includes", true).
  13. Perform ! CreateDataPropertyOrThrow(unscopableList, "keys", true).
  14. Perform ! CreateDataPropertyOrThrow(unscopableList, "toReversed", true).
  15. Perform ! CreateDataPropertyOrThrow(unscopableList, "toSorted", true).
  16. Perform ! CreateDataPropertyOrThrow(unscopableList, "toSpliced", true).
  17. Perform ! CreateDataPropertyOrThrow(unscopableList, "values", true).
  18. Return unscopableList.

This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: true }.

Note

The own property names of this object are property names that were not included as standard properties of Array.prototype prior to the ECMAScript 2015 specification. These names are ignored for with statement binding purposes in order to preserve the behaviour of existing code that might use one of these names as a binding in an outer scope that is shadowed by a with statement whose binding object is an Array.

The reason that "with" is not included in the unscopableList is because it is already a reserved word.

23.1.4 Properties of Array Instances

Array instances are Array exotic objects and have the internal methods specified for such objects. Array instances inherit properties from the Array prototype object.

Array instances have a "length" property, and a set of enumerable properties with array index names.

23.1.4.1 length

The "length" property of an Array instance is a data property whose value is always numerically greater than the name of every configurable own property whose name is an array index.

The "length" property initially has the attributes { [[Writable]]: true, [[Enumerable]]: false, [[Configurable]]: false }.

Note

Reducing the value of the "length" property has the side-effect of deleting own array elements whose array index is between the old and new length values. However, non-configurable properties can not be deleted. Attempting to set the "length" property of an Array to a value that is numerically less than or equal to the largest numeric own property name of an existing non-configurable array-indexed property of the array will result in the length being set to a numeric value that is one greater than that non-configurable numeric own property name. See 10.4.2.1.

23.1.5 Array Iterator Objects

An Array Iterator is an object that represents a specific iteration over some specific Array instance object. There is not a named constructor for Array Iterator objects. Instead, Array Iterator objects are created by calling certain methods of Array instance objects.

23.1.5.1 CreateArrayIterator ( array, kind )

The abstract operation CreateArrayIterator takes arguments array (an Object) and kind (key+value, key, or value) and returns an Object. It is used to create iterator objects for Array methods that return such iterators. It performs the following steps when called:

  1. Let iterator be OrdinaryObjectCreate(%ArrayIteratorPrototype%, « [[IteratedArrayLike]], [[ArrayLikeNextIndex]], [[ArrayLikeIterationKind]] »).
  2. Set iterator.[[IteratedArrayLike]] to array.
  3. Set iterator.[[ArrayLikeNextIndex]] to 0.
  4. Set iterator.[[ArrayLikeIterationKind]] to kind.
  5. Return iterator.

23.1.5.2 The %ArrayIteratorPrototype% Object

The %ArrayIteratorPrototype% object:

23.1.5.2.1 %ArrayIteratorPrototype%.next ( )

  1. Let iteratorObj be the this value.
  2. If iteratorObj is not an Object, throw a TypeError exception.
  3. If iteratorObj does not have all of the internal slots of an Array Iterator Instance (23.1.5.3), throw a TypeError exception.
  4. Let array be iteratorObj.[[IteratedArrayLike]].
  5. If array is undefined, return CreateIteratorResultObject(undefined, true).
  6. Let index be iteratorObj.[[ArrayLikeNextIndex]].
  7. Let kind be iteratorObj.[[ArrayLikeIterationKind]].
  8. If array has a [[TypedArrayName]] internal slot, then
    1. Let taRecord be ? ValidateTypedArrayBounds(array, seq-cst).
    2. Let length be TypedArrayLength(taRecord).
  9. Else,
    1. Let length be ? LengthOfArrayLike(array).
  10. If index ≥ length, then
    1. Set iteratorObj.[[IteratedArrayLike]] to undefined.
    2. Return CreateIteratorResultObject(undefined, true).
  11. Set iteratorObj.[[ArrayLikeNextIndex]] to index + 1.
  12. Let indexNumber be 𝔽(index).
  13. If kind is key, then
    1. Let result be indexNumber.
  14. Else,
    1. Let elementKey be ! ToString(indexNumber).
    2. Let elementValue be ? Get(array, elementKey).
    3. If kind is value, then
      1. Let result be elementValue.
    4. Else,
      1. Assert: kind is key+value.
      2. Let result be CreateArrayFromList(« indexNumber, elementValue »).
  15. Return CreateIteratorResultObject(result, false).

23.1.5.2.2 %ArrayIteratorPrototype% [ %Symbol.toStringTag% ]

The initial value of the %Symbol.toStringTag% property is the String value "Array Iterator".

This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: true }.

23.1.5.3 Properties of Array Iterator Instances

Array Iterator instances are ordinary objects that inherit properties from the %ArrayIteratorPrototype% intrinsic object. Array Iterator instances are initially created with the internal slots listed in Table 70.

Table 70: Internal Slots of Array Iterator Instances
Internal Slot Type Description
[[IteratedArrayLike]] an Object or undefined The array-like object that is being iterated.
[[ArrayLikeNextIndex]] a non-negative integer The integer index of the next element to be examined by this iterator.
[[ArrayLikeIterationKind]] key+value, key, or value A value that identifies what is returned for each element of the iteration.

23.2 TypedArray Objects

A TypedArray presents an array-like view of an underlying binary data buffer (25.1). A TypedArray element type is the underlying binary scalar data type that all elements of a TypedArray instance have. There is a distinct TypedArray constructor, listed in Table 71, for each of the supported element types. Each constructor in Table 71 has a corresponding distinct prototype object.

Table 71: The TypedArray Constructors
Constructor Name and Intrinsic Element Type Element Size Conversion Operation Description
Int8Array
%Int8Array% 		int8 1 ToInt8 8-bit two's complement signed integer
Uint8Array
%Uint8Array% 		uint8 1 ToUint8 8-bit unsigned integer
Uint8ClampedArray
%Uint8ClampedArray% 		uint8clamped 1 ToUint8Clamp 8-bit unsigned integer (clamped conversion)
Int16Array
%Int16Array% 		int16 2 ToInt16 16-bit two's complement signed integer
Uint16Array
%Uint16Array% 		uint16 2 ToUint16 16-bit unsigned integer
Int32Array
%Int32Array% 		int32 4 ToInt32 32-bit two's complement signed integer
Uint32Array
%Uint32Array% 		uint32 4 ToUint32 32-bit unsigned integer
BigInt64Array
%BigInt64Array% 		bigint64 8 ToBigInt64 64-bit two's complement signed integer
BigUint64Array
%BigUint64Array% 		biguint64 8 ToBigUint64 64-bit unsigned integer
Float16Array
%Float16Array% 		float16 2 16-bit IEEE floating point
Float32Array
%Float32Array% 		float32 4 32-bit IEEE floating point
Float64Array
%Float64Array% 		float64 8 64-bit IEEE floating point

In the definitions below, references to TypedArray should be replaced with the appropriate constructor name from the above table.

23.2.1 The %TypedArray% Intrinsic Object

The %TypedArray% intrinsic object:

23.2.1.1 %TypedArray% ( )

This function performs the following steps when called:

  1. Throw a TypeError exception.

The "length" property of this function is +0𝔽.

23.2.2 Properties of the %TypedArray% Intrinsic Object

The %TypedArray% intrinsic object:

  • has a [[Prototype]] internal slot whose value is %Function.prototype%.
  • has a "name" property whose value is "TypedArray".
  • has the following properties:

23.2.2.1 %TypedArray%.from ( source [ , mapper [ , thisArg ] ] )

This method performs the following steps when called:

  1. Let ctor be the this value.
  2. If IsConstructor(ctor) is false, throw a TypeError exception.
  3. If mapper is undefined, then
    1. Let mapping be false.
  4. Else,
    1. If IsCallable(mapper) is false, throw a TypeError exception.
    2. Let mapping be true.
  5. Let usingIterator be ? GetMethod(source, %Symbol.iterator%).
  6. If usingIterator is not undefined, then
    1. Let values be ? IteratorToList(? GetIteratorFromMethod(source, usingIterator)).
    2. Let length be the number of elements in values.
    3. Let targetObj be ? TypedArrayCreateFromConstructor(ctor, « 𝔽(length) »).
    4. Let k be 0.
    5. Repeat, while k < length,
      1. Let kValue be values[k].
      2. If mapping is true, then
        1. Let mappedValue be ? Call(mapper, thisArg, « kValue, 𝔽(k) »).
      3. Else,
        1. Let mappedValue be kValue.
      4. Perform ? TypedArraySetElement(targetObj, 𝔽(k), mappedValue).
      5. Set k to k + 1.
    6. Return targetObj.
  7. NOTE: source is not an iterable object, so assume it is already an array-like object.
  8. Let arrayLike be ! ToObject(source).
  9. Let length be ? LengthOfArrayLike(arrayLike).
  10. Let targetObj be ? TypedArrayCreateFromConstructor(ctor, « 𝔽(length) »).
  11. Let k be 0.
  12. Repeat, while k < length,
    1. Let propertyKey be ! ToString(𝔽(k)).
    2. Let kValue be ? Get(arrayLike, propertyKey).
    3. If mapping is true, then
      1. Let mappedValue be ? Call(mapper, thisArg, « kValue, 𝔽(k) »).
    4. Else,
      1. Let mappedValue be kValue.
    5. Perform ? TypedArraySetElement(targetObj, 𝔽(k), mappedValue).
    6. Set k to k + 1.
  13. Return targetObj.

23.2.2.2 %TypedArray%.of ( ...items )

This method performs the following steps when called:

  1. Let length be the number of elements in items.
  2. Let ctor be the this value.
  3. If IsConstructor(ctor) is false, throw a TypeError exception.
  4. Let newObj be ? TypedArrayCreateFromConstructor(ctor, « 𝔽(length) »).
  5. Let k be 0.
  6. Repeat, while k < length,
    1. Let kValue be items[k].
    2. Perform ? TypedArraySetElement(newObj, 𝔽(k), kValue).
    3. Set k to k + 1.
  7. Return newObj.

23.2.2.3 %TypedArray%.prototype

The initial value of %TypedArray%.prototype is the %TypedArray% prototype object.

This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: false }.

23.2.2.4 get %TypedArray% [ %Symbol.species% ]

%TypedArray%[%Symbol.species%] is an accessor property whose set accessor function is undefined. Its get accessor function performs the following steps when called:

  1. Return the this value.

The value of the "name" property of this function is "get [Symbol.species]".

Note

%TypedArray.prototype% methods normally use their this value's constructor to create a derived object. However, a subclass constructor may over-ride that default behaviour by redefining its %Symbol.species% property.

23.2.3 Properties of the %TypedArray% Prototype Object

The %TypedArray% prototype object:

  • has a [[Prototype]] internal slot whose value is %Object.prototype%.
  • is %TypedArray.prototype%.
  • is an ordinary object.
  • does not have a [[ViewedArrayBuffer]] or any other of the internal slots that are specific to TypedArray instance objects.

23.2.3.1 %TypedArray%.prototype.at ( index )

  1. Let obj be the this value.
  2. Let taRecord be ? ValidateTypedArray(obj, seq-cst).
  3. Let length be TypedArrayLength(taRecord).
  4. Let k be ? ToAbsoluteIndex(index, length).
  5. If k < 0 or k ≥ length, return undefined.
  6. Return TypedArrayGetElement(obj, 𝔽(k)).

23.2.3.2 get %TypedArray%.prototype.buffer

%TypedArray%.prototype.buffer is an accessor property whose set accessor function is undefined. Its get accessor function performs the following steps when called:

  1. Let obj be the this value.
  2. Perform ? RequireInternalSlot(obj, [[TypedArrayName]]).
  3. Assert: obj has a [[ViewedArrayBuffer]] internal slot.
  4. Let buffer be obj.[[ViewedArrayBuffer]].
  5. Return buffer.

23.2.3.3 get %TypedArray%.prototype.byteLength

%TypedArray%.prototype.byteLength is an accessor property whose set accessor function is undefined. Its get accessor function performs the following steps when called:

  1. Let obj be the this value.
  2. Perform ? RequireInternalSlot(obj, [[TypedArrayName]]).
  3. Assert: obj has a [[ViewedArrayBuffer]] internal slot.
  4. Let taRecord be MakeTypedArrayWithBufferWitnessRecord(obj, seq-cst).
  5. If IsTypedArrayOutOfBounds(taRecord) is true, return +0𝔽.
  6. Let size be TypedArrayByteLength(taRecord).
  7. Return 𝔽(size).

23.2.3.4 get %TypedArray%.prototype.byteOffset

%TypedArray%.prototype.byteOffset is an accessor property whose set accessor function is undefined. Its get accessor function performs the following steps when called:

  1. Let obj be the this value.
  2. Perform ? RequireInternalSlot(obj, [[TypedArrayName]]).
  3. Assert: obj has a [[ViewedArrayBuffer]] internal slot.
  4. Let taRecord be MakeTypedArrayWithBufferWitnessRecord(obj, seq-cst).
  5. If IsTypedArrayOutOfBounds(taRecord) is true, return +0𝔽.
  6. Let offset be obj.[[ByteOffset]].
  7. Return 𝔽(offset).

23.2.3.5 %TypedArray%.prototype.constructor

The initial value of %TypedArray%.prototype.constructor is %TypedArray%.

23.2.3.6 %TypedArray%.prototype.copyWithin ( target, start [ , end ] )

The interpretation and use of the arguments of this method are the same as for Array.prototype.copyWithin as defined in 23.1.3.4.

This method performs the following steps when called:

  1. Let obj be the this value.
  2. Let taRecord be ? ValidateTypedArray(obj, seq-cst).
  3. Let length be TypedArrayLength(taRecord).
  4. Let targetIndex be ? ToClampedIndex(target, length).
  5. Let startIndex be ? ToClampedIndex(start, length).
  6. If end is undefined, let endIndex be length; else let endIndex be ? ToClampedIndex(end, length).
  7. Let count be min(endIndex - startIndex, length - targetIndex).
  8. If count > 0, then
    1. NOTE: The copying must be performed in a manner that preserves the bit-level encoding of the source data.
    2. Let buffer be obj.[[ViewedArrayBuffer]].
    3. Set taRecord to ? ValidateTypedArrayBounds(obj, seq-cst).
    4. Set length to TypedArrayLength(taRecord).
    5. NOTE: Side-effects of the above steps may have reduced the size of obj, in which case copying should proceed with the longest still-applicable prefix.
    6. Set count to min(count, length - startIndex, length - targetIndex).
    7. Let elementSize be TypedArrayElementSize(obj).
    8. Let byteOffset be obj.[[ByteOffset]].
    9. Let toByteIndex be (targetIndex × elementSize) + byteOffset.
    10. Let fromByteIndex be (startIndex × elementSize) + byteOffset.
    11. Let countBytes be count × elementSize.
    12. If fromByteIndex < toByteIndex and toByteIndex < fromByteIndex + countBytes, then
      1. Let direction be -1.
      2. Set fromByteIndex to fromByteIndex + countBytes - 1.
      3. Set toByteIndex to toByteIndex + countBytes - 1.
    13. Else,
      1. Let direction be 1.
    14. Repeat, while countBytes > 0,
      1. Assert: fromByteIndex ≥ 0 and toByteIndex ≥ 0.
      2. Let value be GetValueFromBuffer(buffer, fromByteIndex, uint8, true, unordered).
      3. Perform SetValueInBuffer(buffer, toByteIndex, uint8, value, true, unordered).
      4. Set fromByteIndex to fromByteIndex + direction.
      5. Set toByteIndex to toByteIndex + direction.
      6. Set countBytes to countBytes - 1.
  9. Return obj.

23.2.3.7 %TypedArray%.prototype.entries ( )

This method performs the following steps when called:

  1. Let obj be the this value.
  2. Perform ? ValidateTypedArray(obj, seq-cst).
  3. Return CreateArrayIterator(obj, key+value).

23.2.3.8 %TypedArray%.prototype.every ( callback [ , thisArg ] )

The interpretation and use of the arguments of this method are the same as for Array.prototype.every as defined in 23.1.3.6.

This method performs the following steps when called:

  1. Let obj be the this value.
  2. Let taRecord be ? ValidateTypedArray(obj, seq-cst).
  3. Let length be TypedArrayLength(taRecord).
  4. If IsCallable(callback) is false, throw a TypeError exception.
  5. Let k be 0.
  6. Repeat, while k < length,
    1. Let kValue be TypedArrayGetElement(obj, 𝔽(k)).
    2. Let testResult be ToBoolean(? Call(callback, thisArg, « kValue, 𝔽(k), obj »)).
    3. If testResult is false, return false.
    4. Set k to k + 1.
  7. Return true.

This method is not generic. The this value must be an object with a [[TypedArrayName]] internal slot.

23.2.3.9 %TypedArray%.prototype.fill ( value [ , start [ , end ] ] )

The interpretation and use of the arguments of this method are the same as for Array.prototype.fill as defined in 23.1.3.7.

This method performs the following steps when called:

  1. Let obj be the this value.
  2. Let taRecord be ? ValidateTypedArray(obj, seq-cst).
  3. Let length be TypedArrayLength(taRecord).
  4. If obj.[[ContentType]] is bigint, set value to ? ToBigInt(value).
  5. Else, set value to ? ToNumber(value).
  6. Let startIndex be ? ToClampedIndex(start, length).
  7. If end is undefined, let endIndex be length; else let endIndex be ? ToClampedIndex(end, length).
  8. Set taRecord to ? ValidateTypedArrayBounds(obj, seq-cst).
  9. Set length to TypedArrayLength(taRecord).
  10. Set endIndex to min(endIndex, length).
  11. Let k be startIndex.
  12. Repeat, while k < endIndex,
    1. Perform ! TypedArraySetElement(obj, 𝔽(k), value).
    2. Set k to k + 1.
  13. Return obj.

23.2.3.10 %TypedArray%.prototype.filter ( callback [ , thisArg ] )

The interpretation and use of the arguments of this method are the same as for Array.prototype.filter as defined in 23.1.3.8.

This method performs the following steps when called:

  1. Let obj be the this value.
  2. Let taRecord be ? ValidateTypedArray(obj, seq-cst).
  3. Let length be TypedArrayLength(taRecord).
  4. If IsCallable(callback) is false, throw a TypeError exception.
  5. Let kept be a new empty List.
  6. Let captured be 0.
  7. Let k be 0.
  8. Repeat, while k < length,
    1. Let kValue be TypedArrayGetElement(obj, 𝔽(k)).
    2. Let selected be ToBoolean(? Call(callback, thisArg, « kValue, 𝔽(k), obj »)).
    3. If selected is true, then
      1. Append kValue to kept.
      2. Set captured to captured + 1.
    4. Set k to k + 1.
  9. Let result be ? TypedArraySpeciesCreate(obj, « 𝔽(captured) »).
  10. Let n be 0.
  11. For each element element of kept, do
    1. NOTE: element may be undefined if invoking callback detaches or shrinks the buffer backing obj.
    2. Perform ? TypedArraySetElement(result, 𝔽(n), element).
    3. Set n to n + 1.
  12. Return result.

This method is not generic. The this value must be an object with a [[TypedArrayName]] internal slot.

23.2.3.11 %TypedArray%.prototype.find ( predicate [ , thisArg ] )

The interpretation and use of the arguments of this method are the same as for Array.prototype.find as defined in 23.1.3.9.

This method performs the following steps when called:

  1. Let obj be the this value.
  2. Let taRecord be ? ValidateTypedArray(obj, seq-cst).
  3. Let length be TypedArrayLength(taRecord).
  4. Let findRecord be ? FindViaPredicate(obj, length, ascending, predicate, thisArg).
  5. Return findRecord.[[Value]].

This method is not generic. The this value must be an object with a [[TypedArrayName]] internal slot.

23.2.3.12 %TypedArray%.prototype.findIndex ( predicate [ , thisArg ] )

The interpretation and use of the arguments of this method are the same as for Array.prototype.findIndex as defined in 23.1.3.10.

This method performs the following steps when called:

  1. Let obj be the this value.
  2. Let taRecord be ? ValidateTypedArray(obj, seq-cst).
  3. Let length be TypedArrayLength(taRecord).
  4. Let findRecord be ? FindViaPredicate(obj, length, ascending, predicate, thisArg).
  5. Return findRecord.[[Index]].

This method is not generic. The this value must be an object with a [[TypedArrayName]] internal slot.

23.2.3.13 %TypedArray%.prototype.findLast ( predicate [ , thisArg ] )

The interpretation and use of the arguments of this method are the same as for Array.prototype.findLast as defined in 23.1.3.11.

This method performs the following steps when called:

  1. Let obj be the this value.
  2. Let taRecord be ? ValidateTypedArray(obj, seq-cst).
  3. Let length be TypedArrayLength(taRecord).
  4. Let findRecord be ? FindViaPredicate(obj, length, descending, predicate, thisArg).
  5. Return findRecord.[[Value]].

This method is not generic. The this value must be an object with a [[TypedArrayName]] internal slot.

23.2.3.14 %TypedArray%.prototype.findLastIndex ( predicate [ , thisArg ] )

The interpretation and use of the arguments of this method are the same as for Array.prototype.findLastIndex as defined in 23.1.3.12.

This method performs the following steps when called:

  1. Let obj be the this value.
  2. Let taRecord be ? ValidateTypedArray(obj, seq-cst).
  3. Let length be TypedArrayLength(taRecord).
  4. Let findRecord be ? FindViaPredicate(obj, length, descending, predicate, thisArg).
  5. Return findRecord.[[Index]].

This method is not generic. The this value must be an object with a [[TypedArrayName]] internal slot.

23.2.3.15 %TypedArray%.prototype.forEach ( callback [ , thisArg ] )

The interpretation and use of the arguments of this method are the same as for Array.prototype.forEach as defined in 23.1.3.15.

This method performs the following steps when called:

  1. Let obj be the this value.
  2. Let taRecord be ? ValidateTypedArray(obj, seq-cst).
  3. Let length be TypedArrayLength(taRecord).
  4. If IsCallable(callback) is false, throw a TypeError exception.
  5. Let k be 0.
  6. Repeat, while k < length,
    1. Let kValue be TypedArrayGetElement(obj, 𝔽(k)).
    2. Perform ? Call(callback, thisArg, « kValue, 𝔽(k), obj »).
    3. Set k to k + 1.
  7. Return undefined.

This method is not generic. The this value must be an object with a [[TypedArrayName]] internal slot.

23.2.3.16 %TypedArray%.prototype.includes ( searchElement [ , fromIndex ] )

The interpretation and use of the arguments of this method are the same as for Array.prototype.includes as defined in 23.1.3.16.

This method performs the following steps when called:

  1. Let obj be the this value.
  2. Let taRecord be ? ValidateTypedArray(obj, seq-cst).
  3. Let length be TypedArrayLength(taRecord).
  4. If length = 0, return false.
  5. Let k be ? ToClampedIndex(fromIndex, length).
  6. Repeat, while k < length,
    1. Let elementK be TypedArrayGetElement(obj, 𝔽(k)).
    2. If SameValueZero(searchElement, elementK) is true, return true.
    3. Set k to k + 1.
  7. Return false.

This method is not generic. The this value must be an object with a [[TypedArrayName]] internal slot.

23.2.3.17 %TypedArray%.prototype.indexOf ( searchElement [ , fromIndex ] )

The interpretation and use of the arguments of this method are the same as for Array.prototype.indexOf as defined in 23.1.3.17.

This method performs the following steps when called:

  1. Let obj be the this value.
  2. Let taRecord be ? ValidateTypedArray(obj, seq-cst).
  3. Let length be TypedArrayLength(taRecord).
  4. If length = 0, return -1𝔽.
  5. Let k be ? ToClampedIndex(fromIndex, length).
  6. Repeat, while k < length,
    1. Let propertyKey be ! ToString(𝔽(k)).
    2. Let kPresent be ! HasProperty(obj, propertyKey).
    3. If kPresent is true, then
      1. Let elementK be TypedArrayGetElement(obj, 𝔽(k)).
      2. If IsStrictlyEqual(searchElement, elementK) is true, return 𝔽(k).
    4. Set k to k + 1.
  7. Return -1𝔽.

This method is not generic. The this value must be an object with a [[TypedArrayName]] internal slot.

23.2.3.18 %TypedArray%.prototype.join ( separator )

The interpretation and use of the arguments of this method are the same as for Array.prototype.join as defined in 23.1.3.18.

This method performs the following steps when called:

  1. Let obj be the this value.
  2. Let taRecord be ? ValidateTypedArray(obj, seq-cst).
  3. Let length be TypedArrayLength(taRecord).
  4. If separator is undefined, let separatorString be ","; else let separatorString be ? ToString(separator).
  5. Return ? JoinIndexedProperties(obj, length, separatorString).

This method is not generic. The this value must be an object with a [[TypedArrayName]] internal slot.

23.2.3.19 %TypedArray%.prototype.keys ( )

This method performs the following steps when called:

  1. Let obj be the this value.
  2. Perform ? ValidateTypedArray(obj, seq-cst).
  3. Return CreateArrayIterator(obj, key).

23.2.3.20 %TypedArray%.prototype.lastIndexOf ( searchElement [ , fromIndex ] )

The interpretation and use of the arguments of this method are the same as for Array.prototype.lastIndexOf as defined in 23.1.3.20.

This method performs the following steps when called:

  1. Let obj be the this value.
  2. Let taRecord be ? ValidateTypedArray(obj, seq-cst).
  3. Let length be TypedArrayLength(taRecord).
  4. If length = 0, return -1𝔽.
  5. If fromIndex is not present, let k be length - 1; else let k be min(? ToAbsoluteIndex(fromIndex, length), length - 1).
  6. Repeat, while k ≥ 0,
    1. Let propertyKey be ! ToString(𝔽(k)).
    2. Let kPresent be ! HasProperty(obj, propertyKey).
    3. If kPresent is true, then
      1. Let elementK be TypedArrayGetElement(obj, 𝔽(k)).
      2. If IsStrictlyEqual(searchElement, elementK) is true, return 𝔽(k).
    4. Set k to k - 1.
  7. Return -1𝔽.

This method is not generic. The this value must be an object with a [[TypedArrayName]] internal slot.

23.2.3.21 get %TypedArray%.prototype.length

%TypedArray%.prototype.length is an accessor property whose set accessor function is undefined. Its get accessor function performs the following steps when called:

  1. Let obj be the this value.
  2. Perform ? RequireInternalSlot(obj, [[TypedArrayName]]).
  3. Assert: obj has [[ViewedArrayBuffer]] and [[ArrayLength]] internal slots.
  4. Let taRecord be MakeTypedArrayWithBufferWitnessRecord(obj, seq-cst).
  5. If IsTypedArrayOutOfBounds(taRecord) is true, return +0𝔽.
  6. Let length be TypedArrayLength(taRecord).
  7. Return 𝔽(length).

This function is not generic. The this value must be an object with a [[TypedArrayName]] internal slot.

23.2.3.22 %TypedArray%.prototype.map ( callback [ , thisArg ] )

The interpretation and use of the arguments of this method are the same as for Array.prototype.map as defined in 23.1.3.21.

This method performs the following steps when called:

  1. Let obj be the this value.
  2. Let taRecord be ? ValidateTypedArray(obj, seq-cst).
  3. Let length be TypedArrayLength(taRecord).
  4. If IsCallable(callback) is false, throw a TypeError exception.
  5. Let result be ? TypedArraySpeciesCreate(obj, « 𝔽(length) »).
  6. Let k be 0.
  7. Repeat, while k < length,
    1. Let kValue be TypedArrayGetElement(obj, 𝔽(k)).
    2. Let mappedValue be ? Call(callback, thisArg, « kValue, 𝔽(k), obj »).
    3. Perform ? TypedArraySetElement(result, 𝔽(k), mappedValue).
    4. Set k to k + 1.
  8. Return result.

This method is not generic. The this value must be an object with a [[TypedArrayName]] internal slot.

23.2.3.23 %TypedArray%.prototype.reduce ( callback [ , initialValue ] )

The interpretation and use of the arguments of this method are the same as for Array.prototype.reduce as defined in 23.1.3.24.

This method performs the following steps when called:

  1. Let obj be the this value.
  2. Let taRecord be ? ValidateTypedArray(obj, seq-cst).
  3. Let length be TypedArrayLength(taRecord).
  4. If IsCallable(callback) is false, throw a TypeError exception.
  5. If length = 0 and initialValue is not present, throw a TypeError exception.
  6. Let k be 0.
  7. Let accumulator be undefined.
  8. If initialValue is present, then
    1. Set accumulator to initialValue.
  9. Else,
    1. Set accumulator to TypedArrayGetElement(obj, 𝔽(k)).
    2. Set k to k + 1.
  10. Repeat, while k < length,
    1. Let kValue be TypedArrayGetElement(obj, 𝔽(k)).
    2. Set accumulator to ? Call(callback, undefined, « accumulator, kValue, 𝔽(k), obj »).
    3. Set k to k + 1.
  11. Return accumulator.

This method is not generic. The this value must be an object with a [[TypedArrayName]] internal slot.

23.2.3.24 %TypedArray%.prototype.reduceRight ( callback [ , initialValue ] )

The interpretation and use of the arguments of this method are the same as for Array.prototype.reduceRight as defined in 23.1.3.25.

This method performs the following steps when called:

  1. Let obj be the this value.
  2. Let taRecord be ? ValidateTypedArray(obj, seq-cst).
  3. Let length be TypedArrayLength(taRecord).
  4. If IsCallable(callback) is false, throw a TypeError exception.
  5. If length = 0 and initialValue is not present, throw a TypeError exception.
  6. Let k be length - 1.
  7. Let accumulator be undefined.
  8. If initialValue is present, then
    1. Set accumulator to initialValue.
  9. Else,
    1. Set accumulator to TypedArrayGetElement(obj, 𝔽(k)).
    2. Set k to k - 1.
  10. Repeat, while k ≥ 0,
    1. Let kValue be TypedArrayGetElement(obj, 𝔽(k)).
    2. Set accumulator to ? Call(callback, undefined, « accumulator, kValue, 𝔽(k), obj »).
    3. Set k to k - 1.
  11. Return accumulator.

This method is not generic. The this value must be an object with a [[TypedArrayName]] internal slot.

23.2.3.25 %TypedArray%.prototype.reverse ( )

The interpretation and use of the arguments of this method are the same as for Array.prototype.reverse as defined in 23.1.3.26.

This method performs the following steps when called:

  1. Let obj be the this value.
  2. Let taRecord be ? ValidateTypedArray(obj, seq-cst).
  3. Let length be TypedArrayLength(taRecord).
  4. Let middle be floor(length / 2).
  5. Let lower be 0.
  6. Repeat, while lower ≠ middle,
    1. Let upper be length - lower - 1.
    2. Let lowerValue be TypedArrayGetElement(obj, 𝔽(lower)).
    3. Let upperValue be TypedArrayGetElement(obj, 𝔽(upper)).
    4. Perform ! TypedArraySetElement(obj, 𝔽(lower), upperValue).
    5. Perform ! TypedArraySetElement(obj, 𝔽(upper), lowerValue).
    6. Set lower to lower + 1.
  7. Return obj.

This method is not generic. The this value must be an object with a [[TypedArrayName]] internal slot.

23.2.3.26 %TypedArray%.prototype.set ( source [ , offset ] )

This method sets multiple values in this TypedArray, reading the values from source. The details differ based upon the type of source. The optional offset value indicates the first element index in this TypedArray where values are written. If omitted, it is assumed to be 0.

It performs the following steps when called:

  1. Let target be the this value.
  2. Perform ? RequireInternalSlot(target, [[TypedArrayName]]).
  3. Assert: target has a [[ViewedArrayBuffer]] internal slot.
  4. Let targetOffset be ? ToIntegerOrInfinity(offset).
  5. If targetOffset < 0, throw a RangeError exception.
  6. If source is an Object that has a [[TypedArrayName]] internal slot, then
    1. Perform ? SetTypedArrayFromTypedArray(target, targetOffset, source).
  7. Else,
    1. Perform ? SetTypedArrayFromArrayLike(target, targetOffset, source).
  8. Return undefined.

This method is not generic. The this value must be an object with a [[TypedArrayName]] internal slot.

23.2.3.26.1 SetTypedArrayFromArrayLike ( target, targetOffset, source )

The abstract operation SetTypedArrayFromArrayLike takes arguments target (a TypedArray), targetOffset (a non-negative integer or +∞), and source (an ECMAScript language value, but not a TypedArray) and returns either a normal completion containing unused or a throw completion. It sets multiple values in target, starting at index targetOffset, reading the values from source. It performs the following steps when called:

  1. Let targetRecord be ? ValidateTypedArrayBounds(target, seq-cst).
  2. Let targetLength be TypedArrayLength(targetRecord).
  3. Set source to ? ToObject(source).
  4. Let sourceLength be ? LengthOfArrayLike(source).
  5. If targetOffset = +∞, throw a RangeError exception.
  6. If sourceLength + targetOffset > targetLength, throw a RangeError exception.
  7. Let k be 0.
  8. Repeat, while k < sourceLength,
    1. Let propertyKey be ! ToString(𝔽(k)).
    2. Let value be ? Get(source, propertyKey).
    3. Let targetIndex be 𝔽(targetOffset + k).
    4. Perform ? TypedArraySetElement(target, targetIndex, value).
    5. Set k to k + 1.
  9. Return unused.

23.2.3.26.2 SetTypedArrayFromTypedArray ( target, targetOffset, source )

The abstract operation SetTypedArrayFromTypedArray takes arguments target (a TypedArray), targetOffset (a non-negative integer or +∞), and source (a TypedArray) and returns either a normal completion containing unused or a throw completion. It sets multiple values in target, starting at index targetOffset, reading the values from source. It performs the following steps when called:

  1. Let targetBuffer be target.[[ViewedArrayBuffer]].
  2. Let targetRecord be ? ValidateTypedArrayBounds(target, seq-cst).
  3. Let targetLength be TypedArrayLength(targetRecord).
  4. Let sourceBuffer be source.[[ViewedArrayBuffer]].
  5. Let sourceRecord be ? ValidateTypedArrayBounds(source, seq-cst).
  6. Let sourceLength be TypedArrayLength(sourceRecord).
  7. Let targetType be TypedArrayElementType(target).
  8. Let targetElementSize be TypedArrayElementSize(target).
  9. Let targetByteOffset be target.[[ByteOffset]].
  10. Let sourceType be TypedArrayElementType(source).
  11. Let sourceElementSize be TypedArrayElementSize(source).
  12. Let sourceByteOffset be source.[[ByteOffset]].
  13. If targetOffset = +∞, throw a RangeError exception.
  14. If sourceLength + targetOffset > targetLength, throw a RangeError exception.
  15. If target.[[ContentType]] is not source.[[ContentType]], throw a TypeError exception.
  16. If IsSharedArrayBuffer(sourceBuffer) is true, IsSharedArrayBuffer(targetBuffer) is true, and sourceBuffer.[[ArrayBufferData]] is targetBuffer.[[ArrayBufferData]], let sameSharedArrayBuffer be true; else let sameSharedArrayBuffer be false.
  17. If SameValue(sourceBuffer, targetBuffer) is true or sameSharedArrayBuffer is true, then
    1. Let sourceByteLength be TypedArrayByteLength(sourceRecord).
    2. Set sourceBuffer to ? CloneArrayBuffer(sourceBuffer, sourceByteOffset, sourceByteLength).
    3. Let sourceByteIndex be 0.
  18. Else,
    1. Let sourceByteIndex be sourceByteOffset.
  19. Let targetByteIndex be (targetOffset × targetElementSize) + targetByteOffset.
  20. Let limit be targetByteIndex + (targetElementSize × sourceLength).
  21. If sourceType is targetType, then
    1. NOTE: The transfer must be performed in a manner that preserves the bit-level encoding of the source data.
    2. Repeat, while targetByteIndex < limit,
      1. Let value be GetValueFromBuffer(sourceBuffer, sourceByteIndex, uint8, true, unordered).
      2. Perform SetValueInBuffer(targetBuffer, targetByteIndex, uint8, value, true, unordered).
      3. Set sourceByteIndex to sourceByteIndex + 1.
      4. Set targetByteIndex to targetByteIndex + 1.
  22. Else,
    1. Repeat, while targetByteIndex < limit,
      1. Let value be GetValueFromBuffer(sourceBuffer, sourceByteIndex, sourceType, true, unordered).
      2. Perform SetValueInBuffer(targetBuffer, targetByteIndex, targetType, value, true, unordered).
      3. Set sourceByteIndex to sourceByteIndex + sourceElementSize.
      4. Set targetByteIndex to targetByteIndex + targetElementSize.
  23. Return unused.

23.2.3.27 %TypedArray%.prototype.slice ( start, end )

The interpretation and use of the arguments of this method are the same as for Array.prototype.slice as defined in 23.1.3.28.

This method performs the following steps when called:

  1. Let obj be the this value.
  2. Let taRecord be ? ValidateTypedArray(obj, seq-cst).
  3. Let sourceArrayLength be TypedArrayLength(taRecord).
  4. Let startIndex be ? ToClampedIndex(start, sourceArrayLength).
  5. If end is undefined, let endIndex be sourceArrayLength; else let endIndex be ? ToClampedIndex(end, sourceArrayLength).
  6. Let countBytes be max(endIndex - startIndex, 0).
  7. Let resultArray be ? TypedArraySpeciesCreate(obj, « 𝔽(countBytes) »).
  8. If countBytes > 0, then
    1. Set taRecord to ? ValidateTypedArrayBounds(obj, seq-cst).
    2. Set endIndex to min(endIndex, TypedArrayLength(taRecord)).
    3. Set countBytes to max(endIndex - startIndex, 0).
    4. Let sourceType be TypedArrayElementType(obj).
    5. Let targetType be TypedArrayElementType(resultArray).
    6. If sourceType is targetType, then
      1. NOTE: The transfer must be performed in a manner that preserves the bit-level encoding of the source data.
      2. Let sourceBuffer be obj.[[ViewedArrayBuffer]].
      3. Let targetBuffer be resultArray.[[ViewedArrayBuffer]].
      4. Let elementSize be TypedArrayElementSize(obj).
      5. Let sourceByteOffset be obj.[[ByteOffset]].
      6. Let sourceByteIndex be (startIndex × elementSize) + sourceByteOffset.
      7. Let targetByteIndex be resultArray.[[ByteOffset]].
      8. Let endByteIndex be targetByteIndex + (countBytes × elementSize).
      9. Repeat, while targetByteIndex < endByteIndex,
        1. Let value be GetValueFromBuffer(sourceBuffer, sourceByteIndex, uint8, true, unordered).
        2. Perform SetValueInBuffer(targetBuffer, targetByteIndex, uint8, value, true, unordered).
        3. Set sourceByteIndex to sourceByteIndex + 1.
        4. Set targetByteIndex to targetByteIndex + 1.
    7. Else,
      1. Let n be 0.
      2. Let k be startIndex.
      3. Repeat, while k < endIndex,
        1. Let kValue be TypedArrayGetElement(obj, 𝔽(k)).
        2. Perform ! TypedArraySetElement(resultArray, 𝔽(n), kValue).
        3. Set k to k + 1.
        4. Set n to n + 1.
  9. Return resultArray.

This method is not generic. The this value must be an object with a [[TypedArrayName]] internal slot.

23.2.3.28 %TypedArray%.prototype.some ( callback [ , thisArg ] )

The interpretation and use of the arguments of this method are the same as for Array.prototype.some as defined in 23.1.3.29.

This method performs the following steps when called:

  1. Let obj be the this value.
  2. Let taRecord be ? ValidateTypedArray(obj, seq-cst).
  3. Let length be TypedArrayLength(taRecord).
  4. If IsCallable(callback) is false, throw a TypeError exception.
  5. Let k be 0.
  6. Repeat, while k < length,
    1. Let kValue be TypedArrayGetElement(obj, 𝔽(k)).
    2. Let testResult be ToBoolean(? Call(callback, thisArg, « kValue, 𝔽(k), obj »)).
    3. If testResult is true, return true.
    4. Set k to k + 1.
  7. Return false.

This method is not generic. The this value must be an object with a [[TypedArrayName]] internal slot.

23.2.3.29 %TypedArray%.prototype.sort ( comparator )

This is a distinct method that, except as described below, implements the same requirements as those of Array.prototype.sort as defined in 23.1.3.30. The implementation of this method may be optimized with the knowledge that the this value is an object that has a fixed length and whose integer-indexed properties are not sparse.

This method is not generic. The this value must be an object with a [[TypedArrayName]] internal slot.

It performs the following steps when called:

  1. If comparator is not undefined and IsCallable(comparator) is false, throw a TypeError exception.
  2. Let obj be the this value.
  3. Let taRecord be ? ValidateTypedArray(obj, seq-cst).
  4. Let length be TypedArrayLength(taRecord).
  5. NOTE: The following closure performs a numeric comparison rather than the string comparison used in 23.1.3.30.
  6. Let sortCompare be a new Abstract Closure with parameters (x, y) that captures comparator and performs the following steps when called:
    1. Return ? CompareTypedArrayElements(x, y, comparator).
  7. Let sortedList be ? SortIndexedProperties(obj, length, sortCompare, read-through-holes).
  8. Let j be 0.
  9. Repeat, while j < length,
    1. Perform ! TypedArraySetElement(obj, 𝔽(j), sortedList[j]).
    2. Set j to j + 1.
  10. Return obj.
 Note

Because NaN always compares greater than any other value (see CompareTypedArrayElements), NaN property values always sort to the end of the result when comparator is not provided.

23.2.3.30 %TypedArray%.prototype.subarray ( start, end )

This method returns a new TypedArray whose element type is the element type of this TypedArray and whose ArrayBuffer is the ArrayBuffer of this TypedArray, referencing the elements in the interval from start (inclusive) to end (exclusive). If either start or end is negative, it refers to an index from the end of the array, as opposed to from the beginning.

It performs the following steps when called:

  1. Let obj be the this value.
  2. Perform ? RequireInternalSlot(obj, [[TypedArrayName]]).
  3. Assert: obj has a [[ViewedArrayBuffer]] internal slot.
  4. Let buffer be obj.[[ViewedArrayBuffer]].
  5. Let sourceRecord be MakeTypedArrayWithBufferWitnessRecord(obj, seq-cst).
  6. If IsTypedArrayOutOfBounds(sourceRecord) is true, then
    1. Let sourceLength be 0.
  7. Else,
    1. Let sourceLength be TypedArrayLength(sourceRecord).
  8. Let startIndex be ? ToClampedIndex(start, sourceLength).
  9. Let elementSize be TypedArrayElementSize(obj).
  10. Let sourceByteOffset be obj.[[ByteOffset]].
  11. Let beginByteOffset be sourceByteOffset + (startIndex × elementSize).
  12. If obj.[[ArrayLength]] is auto and end is undefined, then
    1. Return ? TypedArraySpeciesCreate(obj, « buffer, 𝔽(beginByteOffset) »).
  13. If end is undefined, let endIndex be sourceLength; else let endIndex be ? ToClampedIndex(end, sourceLength).
  14. Let newLength be max(endIndex - startIndex, 0).
  15. Return ? TypedArraySpeciesCreate(obj, « buffer, 𝔽(beginByteOffset), 𝔽(newLength) »).

This method is not generic. The this value must be an object with a [[TypedArrayName]] internal slot.

23.2.3.31 %TypedArray%.prototype.toLocaleString ( [ reserved1 [ , reserved2 ] ] )

An ECMAScript implementation that includes the ECMA-402 Internationalization API must implement this method as specified in ECMA-402. Otherwise, the following specification of this method is used.

The interpretation and use of the arguments of this method are the same as for Array.prototype.toLocaleString as defined in 23.1.3.32.

This method performs the following steps when called:

  1. Let obj be the this value.
  2. Let taRecord be ? ValidateTypedArray(obj, seq-cst).
  3. Let length be TypedArrayLength(taRecord).
  4. Return ? JoinIndexedProperties(obj, length, LocalizedListSeparator(), "toLocaleString").

23.2.3.32 %TypedArray%.prototype.toReversed ( )

This method performs the following steps when called:

  1. Let obj be the this value.
  2. Let taRecord be ? ValidateTypedArray(obj, seq-cst).
  3. Let length be TypedArrayLength(taRecord).
  4. Let resultArray be ? TypedArrayCreateSameType(obj, length).
  5. Let k be 0.
  6. Repeat, while k < length,
    1. Let from be length - k - 1.
    2. Let fromValue be TypedArrayGetElement(obj, 𝔽(from)).
    3. Perform ! TypedArraySetElement(resultArray, 𝔽(k), fromValue).
    4. Set k to k + 1.
  7. Return resultArray.

23.2.3.33 %TypedArray%.prototype.toSorted ( comparator )

This method performs the following steps when called:

  1. If comparator is not undefined and IsCallable(comparator) is false, throw a TypeError exception.
  2. Let obj be the this value.
  3. Let taRecord be ? ValidateTypedArray(obj, seq-cst).
  4. Let length be TypedArrayLength(taRecord).
  5. Let resultArray be ? TypedArrayCreateSameType(obj, length).
  6. NOTE: The following closure performs a numeric comparison rather than the string comparison used in 23.1.3.34.
  7. Let sortCompare be a new Abstract Closure with parameters (x, y) that captures comparator and performs the following steps when called:
    1. Return ? CompareTypedArrayElements(x, y, comparator).
  8. Let sortedList be ? SortIndexedProperties(obj, length, sortCompare, read-through-holes).
  9. Let j be 0.
  10. Repeat, while j < length,
    1. Perform ! TypedArraySetElement(resultArray, 𝔽(j), sortedList[j]).
    2. Set j to j + 1.
  11. Return resultArray.

23.2.3.34 %TypedArray%.prototype.toString ( )

The initial value of the "toString" property is %Array.prototype.toString%, defined in 23.1.3.36.

23.2.3.35 %TypedArray%.prototype.values ( )

This method performs the following steps when called:

  1. Let obj be the this value.
  2. Perform ? ValidateTypedArray(obj, seq-cst).
  3. Return CreateArrayIterator(obj, value).

23.2.3.36 %TypedArray%.prototype.with ( index, value )

This method performs the following steps when called:

  1. Let obj be the this value.
  2. Let taRecord be ? ValidateTypedArray(obj, seq-cst).
  3. Let length be TypedArrayLength(taRecord).
  4. Let actualIndex be ? ToAbsoluteIndex(index, length).
  5. If obj.[[ContentType]] is bigint, let numericValue be ? ToBigInt(value).
  6. Else, let numericValue be ? ToNumber(value).
  7. If IsValidIntegerIndex(obj, 𝔽(actualIndex)) is false, throw a RangeError exception.
  8. Let resultArray be ? TypedArrayCreateSameType(obj, length).
  9. Let k be 0.
  10. Repeat, while k < length,
    1. If k = actualIndex, let fromValue be numericValue.
    2. Else, let fromValue be TypedArrayGetElement(obj, 𝔽(k)).
    3. NOTE: fromValue may be undefined if either index or value is an object that runs code when coerced to a Number or a BigInt and that code shrinks the buffer backing obj.
    4. Perform ? TypedArraySetElement(resultArray, 𝔽(k), fromValue).
    5. Set k to k + 1.
  11. Return resultArray.

23.2.3.37 %TypedArray%.prototype [ %Symbol.iterator% ] ( )

The initial value of the %Symbol.iterator% property is %TypedArray.prototype.values%, defined in 23.2.3.35.

23.2.3.38 get %TypedArray%.prototype [ %Symbol.toStringTag% ]

%TypedArray%.prototype[%Symbol.toStringTag%] is an accessor property whose set accessor function is undefined. Its get accessor function performs the following steps when called:

  1. Let obj be the this value.
  2. If obj is not an Object, return undefined.
  3. If obj does not have a [[TypedArrayName]] internal slot, return undefined.
  4. Let name be obj.[[TypedArrayName]].
  5. Assert: name is a String.
  6. Return name.

This property has the attributes { [[Enumerable]]: false, [[Configurable]]: true }.

The initial value of the "name" property of this function is "get [Symbol.toStringTag]".

23.2.4 Abstract Operations for TypedArray Objects

23.2.4.1 TypedArrayCreateFromConstructor ( ctor, argList )

The abstract operation TypedArrayCreateFromConstructor takes arguments ctor (a constructor) and argList (a List of ECMAScript language values) and returns either a normal completion containing a TypedArray or a throw completion. It is used to specify the creation of a new TypedArray using a constructor function. It performs the following steps when called:

  1. Let ta be ? Construct(ctor, argList).
  2. Let taRecord be ? ValidateTypedArray(ta, seq-cst).
  3. Assert: ta has all the internal slots mentioned in Properties of TypedArray Instances.
  4. If the number of elements in argList is 1 and argList[0] is a Number, then
    1. If IsTypedArrayOutOfBounds(taRecord) is true, throw a TypeError exception.
    2. Let length be TypedArrayLength(taRecord).
    3. If length < ℝ(argList[0]), throw a TypeError exception.
  5. Return ta.

23.2.4.2 TypedArrayCreateSameType ( exemplar, length )

The abstract operation TypedArrayCreateSameType takes arguments exemplar (a TypedArray) and length (a non-negative integer) and returns either a normal completion containing a TypedArray or a throw completion. It is used to specify the creation of a new TypedArray using a constructor function that is derived from exemplar. Unlike TypedArraySpeciesCreate, which can construct custom TypedArray subclasses through the use of %Symbol.species%, this operation always uses one of the built-in TypedArray constructors. It performs the following steps when called:

  1. Let ctor be the intrinsic object associated with the constructor name exemplar.[[TypedArrayName]] in Table 71.
  2. Let result be ? TypedArrayCreateFromConstructor(ctor, « 𝔽(length) »).
  3. Assert: result has [[TypedArrayName]] and [[ContentType]] internal slots.
  4. Assert: result.[[ContentType]] is exemplar.[[ContentType]].
  5. Return result.

23.2.4.3 TypedArraySpeciesCreate ( exemplar, argList )

The abstract operation TypedArraySpeciesCreate takes arguments exemplar (a TypedArray) and argList (a List of ECMAScript language values) and returns either a normal completion containing a TypedArray or a throw completion. It is used to specify the creation of a new TypedArray using a constructor function that is derived from exemplar. Unlike ArraySpeciesCreate, which can create non-Array objects through the use of %Symbol.species%, this operation enforces that the constructor function creates an actual TypedArray. It performs the following steps when called:

  1. Let defaultCtor be the intrinsic object associated with the constructor name exemplar.[[TypedArrayName]] in Table 71.
  2. Let ctor be ? SpeciesConstructor(exemplar, defaultCtor).
  3. Let result be ? TypedArrayCreateFromConstructor(ctor, argList).
  4. If result.[[ContentType]] is not exemplar.[[ContentType]], throw a TypeError exception.
  5. Return result.

23.2.4.4 ValidateTypedArray ( obj, order )

The abstract operation ValidateTypedArray takes arguments obj (an ECMAScript language value) and order (seq-cst or unordered) and returns either a normal completion containing a TypedArray With Buffer Witness Record or a throw completion. It performs the following steps when called:

  1. Perform ? RequireInternalSlot(obj, [[TypedArrayName]]).
  2. Assert: obj has a [[ViewedArrayBuffer]] internal slot.
  3. Return ? ValidateTypedArrayBounds(obj, order).

23.2.4.5 ValidateTypedArrayBounds ( ta, order )

The abstract operation ValidateTypedArrayBounds takes arguments ta (a TypedArray) and order (seq-cst or unordered) and returns either a normal completion containing a TypedArray With Buffer Witness Record or a throw completion. It validates that ta does not exceed the bounds of its backing buffer. It performs the following steps when called:

  1. Let taRecord be MakeTypedArrayWithBufferWitnessRecord(ta, order).
  2. If IsTypedArrayOutOfBounds(taRecord) is true, throw a TypeError exception.
  3. Return taRecord.

23.2.4.6 TypedArrayElementSize ( obj )

The abstract operation TypedArrayElementSize takes argument obj (a TypedArray) and returns a non-negative integer. It performs the following steps when called:

  1. Return the Element Size value specified in Table 71 for obj.[[TypedArrayName]].

23.2.4.7 TypedArrayElementType ( obj )

The abstract operation TypedArrayElementType takes argument obj (a TypedArray) and returns a TypedArray element type. It performs the following steps when called:

  1. Return the Element Type value specified in Table 71 for obj.[[TypedArrayName]].

23.2.4.8 CompareTypedArrayElements ( x, y, comparator )

The abstract operation CompareTypedArrayElements takes arguments x (a Number or a BigInt), y (a Number or a BigInt), and comparator (a function object or undefined) and returns either a normal completion containing a Number or an abrupt completion. It performs the following steps when called:

  1. Assert: x is a Number and y is a Number, or x is a BigInt and y is a BigInt.
  2. If comparator is not undefined, then
    1. Let result be ? ToNumber(? Call(comparator, undefined, « x, y »)).
    2. If result is NaN, return +0𝔽.
    3. Return result.
  3. If x is NaN and y is NaN, return +0𝔽.
  4. If x is NaN, return 1𝔽.
  5. If y is NaN, return -1𝔽.
  6. If x < y, return -1𝔽.
  7. If x > y, return 1𝔽.
  8. If x is -0𝔽 and y is +0𝔽, return -1𝔽.
  9. If x is +0𝔽 and y is -0𝔽, return 1𝔽.
  10. Return +0𝔽.
 Note
This performs a numeric comparison rather than the string comparison used in 23.1.3.30.2.

23.2.5 The TypedArray Constructors

Each TypedArray constructor:

  • is an intrinsic object that has the structure described below, differing only in the name used as the constructor name instead of TypedArray, in Table 71, except where otherwise noted.
  • is a function whose behaviour differs based upon the number and types of its arguments. The actual behaviour of a call of TypedArray depends upon the number and kind of arguments that are passed to it.
  • is not intended to be called as a function and will throw an exception when called in that manner.
  • may be used as the value of an extends clause of a class definition. Subclass constructors that intend to inherit the specified TypedArray behaviour must include a super call to the TypedArray constructor to create and initialize the subclass instance with the internal state necessary to support the built-in methods of %TypedArray%.prototype.

23.2.5.1 TypedArray ( ...args )

Each TypedArray constructor performs the following steps when called:

  1. If NewTarget is undefined, throw a TypeError exception.
  2. Let ctorName be the String value of the Constructor Name value specified in Table 71 for this TypedArray constructor.
  3. Let proto be "%TypedArray.prototype%".
  4. Let numberOfArgs be the number of elements in args.
  5. If numberOfArgs = 0, return ? AllocateTypedArray(ctorName, NewTarget, proto, 0).
  6. Let firstArg be args[0].
  7. If firstArg is an Object, then
    1. Let obj be ? AllocateTypedArray(ctorName, NewTarget, proto).
    2. If firstArg has a [[TypedArrayName]] internal slot, then
      1. Perform ? InitializeTypedArrayFromTypedArray(obj, firstArg).
    3. Else if firstArg has an [[ArrayBufferData]] internal slot, then
      1. If numberOfArgs > 1, let byteOffset be args[1]; else let byteOffset be undefined.
      2. If numberOfArgs > 2, let length be args[2]; else let length be undefined.
      3. Perform ? InitializeTypedArrayFromArrayBuffer(obj, firstArg, byteOffset, length).
    4. Else,
      1. Assert: firstArg is an Object and firstArg does not have either a [[TypedArrayName]] or an [[ArrayBufferData]] internal slot.
      2. Perform ? InitializeTypedArrayFromElements(obj, firstArg).
    5. Return obj.
  8. Assert: firstArg is not an Object.
  9. Let elementLength be ? ToIndex(firstArg).
  10. Return ? AllocateTypedArray(ctorName, NewTarget, proto, elementLength).

23.2.5.1.1 AllocateTypedArray ( ctorName, newTarget, defaultProto [ , length ] )

The abstract operation AllocateTypedArray takes arguments ctorName (a String which is the name of a TypedArray constructor in Table 71), newTarget (a constructor), and defaultProto (a String) and optional argument length (a non-negative integer) and returns either a normal completion containing a TypedArray or a throw completion. It is used to validate and create an instance of a TypedArray constructor. If the length argument is passed, an ArrayBuffer of that length is also allocated and associated with the new TypedArray instance. AllocateTypedArray provides common semantics that is used by TypedArray. It performs the following steps when called:

  1. Let proto be ? GetPrototypeFromConstructor(newTarget, defaultProto).
  2. Let obj be TypedArrayCreate(proto).
  3. Assert: obj.[[ViewedArrayBuffer]] is undefined.
  4. Set obj.[[TypedArrayName]] to ctorName.
  5. If ctorName is either "BigInt64Array" or "BigUint64Array", set obj.[[ContentType]] to bigint.
  6. Else, set obj.[[ContentType]] to number.
  7. If length is not present, then
    1. Set obj.[[ByteLength]] to 0.
    2. Set obj.[[ByteOffset]] to 0.
    3. Set obj.[[ArrayLength]] to 0.
  8. Else,
    1. Perform ? AllocateTypedArrayBuffer(obj, length).
  9. Return obj.

23.2.5.1.2 InitializeTypedArrayFromTypedArray ( obj, sourceArray )

The abstract operation InitializeTypedArrayFromTypedArray takes arguments obj (a TypedArray) and sourceArray (a TypedArray) and returns either a normal completion containing unused or a throw completion. It performs the following steps when called:

  1. Let sourceData be sourceArray.[[ViewedArrayBuffer]].
  2. Let elementType be TypedArrayElementType(obj).
  3. Let elementSize be TypedArrayElementSize(obj).
  4. Let sourceType be TypedArrayElementType(sourceArray).
  5. Let sourceElementSize be TypedArrayElementSize(sourceArray).
  6. Let sourceByteOffset be sourceArray.[[ByteOffset]].
  7. Let sourceRecord be ? ValidateTypedArrayBounds(sourceArray, seq-cst).
  8. Let elementLength be TypedArrayLength(sourceRecord).
  9. Let byteLength be elementSize × elementLength.
  10. If elementType is sourceType, then
    1. Let data be ? CloneArrayBuffer(sourceData, sourceByteOffset, byteLength).
  11. Else,
    1. Let data be ? AllocateArrayBuffer(%ArrayBuffer%, byteLength).
    2. If sourceArray.[[ContentType]] is not obj.[[ContentType]], throw a TypeError exception.
    3. Let sourceByteIndex be sourceByteOffset.
    4. Let targetByteIndex be 0.
    5. Let count be elementLength.
    6. Repeat, while count > 0,
      1. Let value be GetValueFromBuffer(sourceData, sourceByteIndex, sourceType, true, unordered).
      2. Perform SetValueInBuffer(data, targetByteIndex, elementType, value, true, unordered).
      3. Set sourceByteIndex to sourceByteIndex + sourceElementSize.
      4. Set targetByteIndex to targetByteIndex + elementSize.
      5. Set count to count - 1.
  12. Set obj.[[ViewedArrayBuffer]] to data.
  13. Set obj.[[ByteLength]] to byteLength.
  14. Set obj.[[ByteOffset]] to 0.
  15. Set obj.[[ArrayLength]] to elementLength.
  16. Return unused.

23.2.5.1.3 InitializeTypedArrayFromArrayBuffer ( obj, buffer, byteOffset, length )

The abstract operation InitializeTypedArrayFromArrayBuffer takes arguments obj (a TypedArray), buffer (an ArrayBuffer or a SharedArrayBuffer), byteOffset (an ECMAScript language value), and length (an ECMAScript language value) and returns either a normal completion containing unused or a throw completion. It performs the following steps when called:

  1. Let elementSize be TypedArrayElementSize(obj).
  2. Let offset be ? ToIndex(byteOffset).
  3. If offset modulo elementSize ≠ 0, throw a RangeError exception.
  4. Let bufferIsFixedLength be IsFixedLengthArrayBuffer(buffer).
  5. If length is not undefined, then
    1. Let newLength be ? ToIndex(length).
  6. If IsDetachedBuffer(buffer) is true, throw a TypeError exception.
  7. Let bufferByteLength be ArrayBufferByteLength(buffer, seq-cst).
  8. If length is undefined and bufferIsFixedLength is false, then
    1. If offset > bufferByteLength, throw a RangeError exception.
    2. Set obj.[[ByteLength]] to auto.
    3. Set obj.[[ArrayLength]] to auto.
  9. Else,
    1. If length is undefined, then
      1. If bufferByteLength modulo elementSize ≠ 0, throw a RangeError exception.
      2. Let newByteLength be bufferByteLength - offset.
      3. If newByteLength < 0, throw a RangeError exception.
    2. Else,
      1. Let newByteLength be newLength × elementSize.
      2. If offset + newByteLength > bufferByteLength, throw a RangeError exception.
    3. Set obj.[[ByteLength]] to newByteLength.
    4. Set obj.[[ArrayLength]] to newByteLength / elementSize.
  10. Set obj.[[ViewedArrayBuffer]] to buffer.
  11. Set obj.[[ByteOffset]] to offset.
  12. Return unused.

23.2.5.1.4 InitializeTypedArrayFromElements ( obj, source )

The abstract operation InitializeTypedArrayFromElements takes arguments obj (a TypedArray) and source (an Object) and returns either a normal completion containing unused or a throw completion. It performs the following steps when called:

  1. Let usingIterator be ? GetMethod(source, %Symbol.iterator%).
  2. If usingIterator is not undefined, then
    1. Let list be ? IteratorToList(? GetIteratorFromMethod(source, usingIterator)).
    2. Let length be the number of elements in list.
  3. Else,
    1. NOTE: source is not iterable, so assume it is an array-like object.
    2. Let length be ? LengthOfArrayLike(source).
  4. Perform ? AllocateTypedArrayBuffer(obj, length).
  5. Let k be 0.
  6. Repeat, while k < length,
    1. If usingIterator is not undefined, then
      1. Let kValue be list[k].
    2. Else,
      1. Let propertyKey be ! ToString(𝔽(k)).
      2. Let kValue be ? Get(source, propertyKey).
    3. Perform ? TypedArraySetElement(obj, 𝔽(k), kValue).
    4. Set k to k + 1.
  7. Return unused.

23.2.5.1.5 AllocateTypedArrayBuffer ( obj, length )

The abstract operation AllocateTypedArrayBuffer takes arguments obj (a TypedArray) and length (a non-negative integer) and returns either a normal completion containing unused or a throw completion. It allocates and associates an ArrayBuffer with obj. It performs the following steps when called:

  1. Assert: obj.[[ViewedArrayBuffer]] is undefined.
  2. Let elementSize be TypedArrayElementSize(obj).
  3. Let byteLength be elementSize × length.
  4. Let data be ? AllocateArrayBuffer(%ArrayBuffer%, byteLength).
  5. Set obj.[[ViewedArrayBuffer]] to data.
  6. Set obj.[[ByteLength]] to byteLength.
  7. Set obj.[[ByteOffset]] to 0.
  8. Set obj.[[ArrayLength]] to length.
  9. Return unused.

23.2.6 Properties of the TypedArray Constructors

Each TypedArray constructor:

  • has a [[Prototype]] internal slot whose value is %TypedArray%.
  • has a "length" property whose value is 3𝔽.
  • has a "name" property whose value is the String value of the constructor name specified for it in Table 71.
  • has the following properties:

23.2.6.1 TypedArray.BYTES_PER_ELEMENT

The value of TypedArray.BYTES_PER_ELEMENT is the Element Size value specified in Table 71 for TypedArray.

This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: false }.

23.2.6.2 TypedArray.prototype

The initial value of TypedArray.prototype is the corresponding TypedArray prototype intrinsic object (23.2.7).

This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: false }.

23.2.7 Properties of the TypedArray Prototype Objects

Each TypedArray prototype object:

  • has a [[Prototype]] internal slot whose value is %TypedArray.prototype%.
  • is an ordinary object.
  • does not have a [[ViewedArrayBuffer]] or any other of the internal slots that are specific to TypedArray instance objects.

23.2.7.1 TypedArray.prototype.BYTES_PER_ELEMENT

The value of TypedArray.prototype.BYTES_PER_ELEMENT is the Element Size value specified in Table 71 for TypedArray.

This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: false }.

23.2.7.2 TypedArray.prototype.constructor

The initial value of the "constructor" property of the prototype for a given TypedArray constructor is the constructor itself.

23.2.8 Properties of TypedArray Instances

TypedArray instances are TypedArrays. Each TypedArray instance inherits properties from the corresponding TypedArray prototype object. Each TypedArray instance has the following internal slots: [[ViewedArrayBuffer]], [[TypedArrayName]], [[ContentType]], [[ByteLength]], [[ByteOffset]], and [[ArrayLength]].

23.3 Uint8Array Objects

A Uint8Array is a particular kind of TypedArray as described above. In addition, there are additional methods on the Uint8Array constructor (23.3.1) and on the Uint8Array prototype object (23.3.2).

23.3.1 Additional Properties of the Uint8Array Constructor

23.3.1.1 Uint8Array.fromBase64 ( string [ , options ] )

  1. If string is not a String, throw a TypeError exception.
  2. Let optionsObj be ? GetOptionsObject(options).
  3. Let alphabet be ? Get(optionsObj, "alphabet").
  4. If alphabet is undefined, set alphabet to "base64".
  5. If alphabet is neither "base64" nor "base64url", throw a TypeError exception.
  6. Let lastChunkHandling be ? Get(optionsObj, "lastChunkHandling").
  7. If lastChunkHandling is undefined, set lastChunkHandling to "loose".
  8. If lastChunkHandling is not one of "loose", "strict", or "stop-before-partial", throw a TypeError exception.
  9. Let result be FromBase64(string, alphabet, lastChunkHandling).
  10. If result.[[Error]] is not none, then
    1. Throw result.[[Error]].
  11. Let resultLength be the number of elements in result.[[Bytes]].
  12. Let ta be ? AllocateTypedArray("Uint8Array", %Uint8Array%, "%Uint8Array.prototype%", resultLength).
  13. Assert: ta.[[ViewedArrayBuffer]].[[ArrayBufferByteLength]] is the number of elements in result.[[Bytes]].
  14. Set the value at each index of ta.[[ViewedArrayBuffer]].[[ArrayBufferData]] to the value at the corresponding index of result.[[Bytes]].
  15. Return ta.

23.3.1.2 Uint8Array.fromHex ( string )

  1. If string is not a String, throw a TypeError exception.
  2. Let result be FromHex(string).
  3. If result.[[Error]] is not none, then
    1. Throw result.[[Error]].
  4. Let resultLength be the number of elements in result.[[Bytes]].
  5. Let ta be ? AllocateTypedArray("Uint8Array", %Uint8Array%, "%Uint8Array.prototype%", resultLength).
  6. Assert: ta.[[ViewedArrayBuffer]].[[ArrayBufferByteLength]] is the number of elements in result.[[Bytes]].
  7. Set the value at each index of ta.[[ViewedArrayBuffer]].[[ArrayBufferData]] to the value at the corresponding index of result.[[Bytes]].
  8. Return ta.

23.3.2 Additional Properties of the Uint8Array Prototype Object

23.3.2.1 Uint8Array.prototype.setFromBase64 ( string [ , options ] )

  1. Let into be the this value.
  2. Perform ? ValidateUint8Array(into).
  3. If string is not a String, throw a TypeError exception.
  4. Let optionsObj be ? GetOptionsObject(options).
  5. Let alphabet be ? Get(optionsObj, "alphabet").
  6. If alphabet is undefined, set alphabet to "base64".
  7. If alphabet is neither "base64" nor "base64url", throw a TypeError exception.
  8. Let lastChunkHandling be ? Get(optionsObj, "lastChunkHandling").
  9. If lastChunkHandling is undefined, set lastChunkHandling to "loose".
  10. If lastChunkHandling is not one of "loose", "strict", or "stop-before-partial", throw a TypeError exception.
  11. Let taRecord be ? ValidateTypedArrayBounds(into, seq-cst).
  12. Let byteLength be TypedArrayLength(taRecord).
  13. Let result be FromBase64(string, alphabet, lastChunkHandling, byteLength).
  14. Let bytes be result.[[Bytes]].
  15. Let written be the number of elements in bytes.
  16. NOTE: FromBase64 does not invoke any user code, so the ArrayBuffer backing into cannot have been detached or shrunk.
  17. Assert: written ≤ byteLength.
  18. Perform SetUint8ArrayBytes(into, bytes).
  19. If result.[[Error]] is not none, then
    1. Throw result.[[Error]].
  20. Let resultObj be OrdinaryObjectCreate(%Object.prototype%).
  21. Perform ! CreateDataPropertyOrThrow(resultObj, "read", 𝔽(result.[[Read]])).
  22. Perform ! CreateDataPropertyOrThrow(resultObj, "written", 𝔽(written)).
  23. Return resultObj.

23.3.2.2 Uint8Array.prototype.setFromHex ( string )

  1. Let into be the this value.
  2. Perform ? ValidateUint8Array(into).
  3. If string is not a String, throw a TypeError exception.
  4. Let taRecord be ? ValidateTypedArrayBounds(into, seq-cst).
  5. Let byteLength be TypedArrayLength(taRecord).
  6. Let result be FromHex(string, byteLength).
  7. Let bytes be result.[[Bytes]].
  8. Let written be the number of elements in bytes.
  9. NOTE: FromHex does not invoke any user code, so the ArrayBuffer backing into cannot have been detached or shrunk.
  10. Assert: written ≤ byteLength.
  11. Perform SetUint8ArrayBytes(into, bytes).
  12. If result.[[Error]] is not none, then
    1. Throw result.[[Error]].
  13. Let resultObj be OrdinaryObjectCreate(%Object.prototype%).
  14. Perform ! CreateDataPropertyOrThrow(resultObj, "read", 𝔽(result.[[Read]])).
  15. Perform ! CreateDataPropertyOrThrow(resultObj, "written", 𝔽(written)).
  16. Return resultObj.

23.3.2.3 Uint8Array.prototype.toBase64 ( [ options ] )

  1. Let obj be the this value.
  2. Perform ? ValidateUint8Array(obj).
  3. Let optionsObj be ? GetOptionsObject(options).
  4. Let alphabet be ? Get(optionsObj, "alphabet").
  5. If alphabet is undefined, set alphabet to "base64".
  6. If alphabet is neither "base64" nor "base64url", throw a TypeError exception.
  7. Let omitPadding be ToBoolean(? Get(optionsObj, "omitPadding")).
  8. Let toEncode be ? GetUint8ArrayBytes(obj).
  9. If alphabet is "base64", then
    1. Let outAscii be the sequence of code points which results from encoding toEncode according to the base64 encoding specified in section 4 of RFC 4648. Padding is included if and only if omitPadding is false.
  10. Else,
    1. Assert: alphabet is "base64url".
    2. Let outAscii be the sequence of code points which results from encoding toEncode according to the base64url encoding specified in section 5 of RFC 4648. Padding is included if and only if omitPadding is false.
  11. Return CodePointsToString(outAscii).

23.3.2.4 Uint8Array.prototype.toHex ( )

  1. Let obj be the this value.
  2. Perform ? ValidateUint8Array(obj).
  3. Let toEncode be ? GetUint8ArrayBytes(obj).
  4. Let out be the empty String.
  5. For each byte byte of toEncode, do
    1. Let hex be Number::toString(𝔽(byte), 16).
    2. Set hex to StringPad(hex, 2, "0", start).
    3. Set out to the string-concatenation of out and hex.
  6. Return out.

23.3.3 Abstract Operations for Uint8Array Objects

23.3.3.1 ValidateUint8Array ( ta )

The abstract operation ValidateUint8Array takes argument ta (an ECMAScript language value) and returns either a normal completion containing unused or a throw completion. It performs the following steps when called:

  1. Perform ? RequireInternalSlot(ta, [[TypedArrayName]]).
  2. If ta.[[TypedArrayName]] is not "Uint8Array", throw a TypeError exception.
  3. Return unused.

23.3.3.2 GetUint8ArrayBytes ( ta )

The abstract operation GetUint8ArrayBytes takes argument ta (a Uint8Array) and returns either a normal completion containing a List of byte values or a throw completion. It performs the following steps when called:

  1. Let buffer be ta.[[ViewedArrayBuffer]].
  2. Let taRecord be ? ValidateTypedArrayBounds(ta, seq-cst).
  3. Let length be TypedArrayLength(taRecord).
  4. Let byteOffset be ta.[[ByteOffset]].
  5. Let bytes be a new empty List.
  6. Let index be 0.
  7. Repeat, while index < length,
    1. Let byteIndex be byteOffset + index.
    2. Let byte be ℝ(GetValueFromBuffer(buffer, byteIndex, uint8, true, unordered)).
    3. Append byte to bytes.
    4. Set index to index + 1.
  8. Return bytes.

23.3.3.3 SetUint8ArrayBytes ( into, bytes )

The abstract operation SetUint8ArrayBytes takes arguments into (a Uint8Array) and bytes (a List of byte values) and returns unused. It performs the following steps when called:

  1. Let offset be into.[[ByteOffset]].
  2. Let length be the number of elements in bytes.
  3. Let index be 0.
  4. Repeat, while index < length,
    1. Let byte be bytes[index].
    2. Let byteIndexInBuffer be index + offset.
    3. Perform SetValueInBuffer(into.[[ViewedArrayBuffer]], byteIndexInBuffer, uint8, 𝔽(byte), true, unordered).
    4. Set index to index + 1.
  5. Return unused.

23.3.3.4 SkipAsciiWhitespace ( string, index )

The abstract operation SkipAsciiWhitespace takes arguments string (a String) and index (a non-negative integer) and returns a non-negative integer. It performs the following steps when called:

  1. Let length be the length of string.
  2. Repeat, while index < length,
    1. Let char be the code unit at index index within string.
    2. If char is not one of 0x0009 (TAB), 0x000A (LF), 0x000C (FF), 0x000D (CR), or 0x0020 (SPACE), then
      1. Return index.
    3. Set index to index + 1.
  3. Return index.

23.3.3.5 DecodeFinalBase64Chunk ( chunk, throwOnExtraBits )

The abstract operation DecodeFinalBase64Chunk takes arguments chunk (a String of length 2 or 3) and throwOnExtraBits (a Boolean) and returns either a normal completion containing a List of byte values, or a throw completion. It performs the following steps when called:

  1. Let chunkLength be the length of chunk.
  2. If chunkLength = 2, then
    1. Set chunk to the string-concatenation of chunk and "AA".
  3. Else,
    1. Assert: chunkLength is 3.
    2. Set chunk to the string-concatenation of chunk and "A".
  4. Let bytes be DecodeFullLengthBase64Chunk(chunk).
  5. If chunkLength = 2, then
    1. If throwOnExtraBits is true and bytes[1] ≠ 0, throw a SyntaxError exception.
    2. Return « bytes[0] ».
  6. If throwOnExtraBits is true and bytes[2] ≠ 0, throw a SyntaxError exception.
  7. Return « bytes[0], bytes[1] ».

23.3.3.6 DecodeFullLengthBase64Chunk ( chunk )

The abstract operation DecodeFullLengthBase64Chunk takes argument chunk (a String of length 4) and returns a List of byte values of length 3.

The standard base64 alphabet is "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/", i.e., the String whose elements are the code units corresponding to every letter and number in the Unicode Basic Latin block along with "+" and "/".

  1. Let byteSequence be the unique sequence of 3 bytes resulting from decoding chunk as base64 (i.e., the sequence such that applying the base64 encoding specified in section 4 of RFC 4648 to byteSequence would produce chunk).
  2. Return a List whose elements are the elements of byteSequence, in order.

23.3.3.7 FromBase64 ( string, alphabet, lastChunkHandling [ , maxLength ] )

The abstract operation FromBase64 takes arguments string (a String), alphabet ("base64" or "base64url"), and lastChunkHandling ("loose", "strict", or "stop-before-partial") and optional argument maxLength (a non-negative integer) and returns a Record with fields [[Read]] (an integer), [[Bytes]] (a List of byte values), and [[Error]] (a SyntaxError object or none). It performs the following steps when called:

  1. If maxLength is not present, then
    1. Set maxLength to 253 - 1.
    2. NOTE: Because the input is a String, the length of Strings is limited to 253 - 1 characters, and the output requires no more bytes than the input has characters, this limit can never be reached. However, it is editorially convenient to use a finite value for maxLength.
  2. NOTE: The order of validation and decoding in the algorithm below is not observable. Implementations are encouraged to perform them in whatever order is most efficient, possibly interleaving validation with decoding.
  3. If maxLength = 0, then
    1. Return the Record { [[Read]]: 0, [[Bytes]]: « », [[Error]]: none }.
  4. Let read be 0.
  5. Let bytes be a new empty List.
  6. Let chunk be the empty String.
  7. Let chunkLength be 0.
  8. Let index be 0.
  9. Let length be the length of string.
  10. Repeat,
    1. Assert: The number of elements in bytes is evenly divisible by 3.
    2. Set index to SkipAsciiWhitespace(string, index).
    3. If index = length, then
      1. If chunkLength > 0, then
        1. If lastChunkHandling is "stop-before-partial", then
          1. Return the Record { [[Read]]: read, [[Bytes]]: bytes, [[Error]]: none }.
        2. If lastChunkHandling is "strict", then
          1. Let error be a newly created SyntaxError object.
          2. Return the Record { [[Read]]: read, [[Bytes]]: bytes, [[Error]]: error }.
        3. Assert: lastChunkHandling is "loose".
        4. If chunkLength = 1, then
          1. Let error be a newly created SyntaxError object.
          2. Return the Record { [[Read]]: read, [[Bytes]]: bytes, [[Error]]: error }.
        5. Set bytes to the list-concatenation of bytes and ! DecodeFinalBase64Chunk(chunk, false).
      2. Return the Record { [[Read]]: length, [[Bytes]]: bytes, [[Error]]: none }.
    4. Let char be the substring of string from index to index + 1.
    5. Set index to index + 1.
    6. If char is "=", then
      1. If chunkLength < 2, then
        1. Let error be a newly created SyntaxError object.
        2. Return the Record { [[Read]]: read, [[Bytes]]: bytes, [[Error]]: error }.
      2. Set index to SkipAsciiWhitespace(string, index).
      3. If chunkLength = 2, then
        1. If index = length, then
          1. If lastChunkHandling is "stop-before-partial", then
            1. Return the Record { [[Read]]: read, [[Bytes]]: bytes, [[Error]]: none }.
          2. Let error be a newly created SyntaxError object.
          3. Return the Record { [[Read]]: read, [[Bytes]]: bytes, [[Error]]: error }.
        2. Set char to the substring of string from index to index + 1.
        3. If char is "=", then
          1. Set index to SkipAsciiWhitespace(string, index + 1).
      4. If index < length, then
        1. Let error be a newly created SyntaxError object.
        2. Return the Record { [[Read]]: read, [[Bytes]]: bytes, [[Error]]: error }.
      5. If lastChunkHandling is "strict", let throwOnExtraBits be true; else let throwOnExtraBits be false.
      6. Let decodeResult be Completion(DecodeFinalBase64Chunk(chunk, throwOnExtraBits)).
      7. If decodeResult is an abrupt completion, then
        1. Let error be decodeResult.[[Value]].
        2. Return the Record { [[Read]]: read, [[Bytes]]: bytes, [[Error]]: error }.
      8. Set bytes to the list-concatenation of bytes and ! decodeResult.
      9. Return the Record { [[Read]]: length, [[Bytes]]: bytes, [[Error]]: none }.
    7. If alphabet is "base64url", then
      1. If char is either "+" or "/", then
        1. Let error be a newly created SyntaxError object.
        2. Return the Record { [[Read]]: read, [[Bytes]]: bytes, [[Error]]: error }.
      2. Else if char is "-", then
        1. Set char to "+".
      3. Else if char is "_", then
        1. Set char to "/".
    8. If the sole code unit of char is not an element of the standard base64 alphabet, then
      1. Let error be a newly created SyntaxError object.
      2. Return the Record { [[Read]]: read, [[Bytes]]: bytes, [[Error]]: error }.
    9. Let remaining be maxLength - the number of elements in bytes.
    10. If remaining = 1 and chunkLength = 2, or if remaining = 2 and chunkLength = 3, then
      1. Return the Record { [[Read]]: read, [[Bytes]]: bytes, [[Error]]: none }.
    11. Set chunk to the string-concatenation of chunk and char.
    12. Set chunkLength to the length of chunk.
    13. If chunkLength = 4, then
      1. Set bytes to the list-concatenation of bytes and DecodeFullLengthBase64Chunk(chunk).
      2. Set chunk to the empty String.
      3. Set chunkLength to 0.
      4. Set read to index.
      5. If the number of elements in bytes = maxLength, then
        1. Return the Record { [[Read]]: read, [[Bytes]]: bytes, [[Error]]: none }.

23.3.3.8 FromHex ( string [ , maxLength ] )

The abstract operation FromHex takes argument string (a String) and optional argument maxLength (a non-negative integer) and returns a Record with fields [[Read]] (an integer), [[Bytes]] (a List of byte values), and [[Error]] (a SyntaxError object or none). It performs the following steps when called:

  1. If maxLength is not present, set maxLength to 253 - 1.
  2. Let length be the length of string.
  3. Let bytes be a new empty List.
  4. Let read be 0.
  5. If length modulo 2 ≠ 0, then
    1. Let error be a newly created SyntaxError object.
    2. Return the Record { [[Read]]: read, [[Bytes]]: bytes, [[Error]]: error }.
  6. Repeat, while read < length and the number of elements in bytes < maxLength,
    1. Let hexits be the substring of string from read to read + 2.
    2. If hexits contains any code units which are not in "0123456789abcdefABCDEF", then
      1. Let error be a newly created SyntaxError object.
      2. Return the Record { [[Read]]: read, [[Bytes]]: bytes, [[Error]]: error }.
    3. Set read to read + 2.
    4. Let byte be the integer value represented by hexits in base-16 notation, using the letters A through F and a through f for digits with values 10 through 15.
    5. Append byte to bytes.
  7. Return the Record { [[Read]]: read, [[Bytes]]: bytes, [[Error]]: none }.