A {{jsxref("Statements/for", "for")}} loop repeats until a specified condition evaluates to false. The JavaScript `for` loop is similar to the Java and C `for` loop.

A `for` statement looks as follows:

When a `for` loop executes, the following occurs:

1. The initializing expression `initialization`, if any, is executed. This expression usually initializes one or more loop counters, but the syntax allows an expression of any degree of complexity. This expression can also declare variables.

2. The `condition` expression is evaluated. If the value of `condition` is true, the loop statements execute. Otherwise, the `for` loop terminates. (If the `condition` expression is omitted entirely, the condition is assumed to be true.)

3. The `statement` executes. To execute multiple statements, use a [block statement](/en-US/docs/Web/JavaScript/Reference/Statements/block) (`{ }`) to group those statements.

4. If present, the update expression `afterthought` is executed.

5. Control returns to Step 2.

In the example below, the function contains a `for` statement that counts

the number of selected options in a scrolling list (a [`<select>`](/en-US/docs/Web/HTML/Reference/Elements/select)

element that allows multiple selections).

<form name="selectForm">

<label for="musicTypes"

>Choose some music types, then click the button below:</label

>

<select id="musicTypes" name="musicTypes" multiple>

<option selected>R&amp;B</option>

<option>Jazz</option>

<option>Blues</option>

<option>New Age</option>

<option>Classical</option>

<option>Opera</option>

</select>

<button id="btn" type="button">How many are selected?</button>

</form>

Here, the `for` statement declares the variable `i` and initializes it to `0`. It checks that `i` is less than the number of options in the `<select>` element, performs the succeeding `if` statement, and increments `i` by 1 after each pass through the loop.

function countSelected(selectObject) {

let numberSelected = 0;

for (let i = 0; i < selectObject.options.length; i++) {

if (selectObject.options[i].selected) {

numberSelected++;

}

}

return numberSelected;

}

const btn = document.getElementById("btn");

btn.addEventListener("click", () => {

const musicTypes = document.selectForm.musicTypes;

console.log(`You have selected ${countSelected(musicTypes)} option(s).`);

});

The {{jsxref("Statements/do...while", "do...while")}} statement repeats until a

specified condition evaluates to false.

A `do...while` statement looks as follows:

`statement` is always executed once before the condition is

checked. (To execute multiple statements, use a block statement (`{ }`)

to group those statements.)

If `condition` is `true`, the statement executes again. At the

end of every execution, the condition is checked. When the condition is

`false`, execution stops, and control passes to the statement following

`do...while`.

In the following example, the `do` loop iterates at least once and

reiterates until `i` is no longer less than `5`.

let i = 0;

do {

i += 1;

console.log(i);

} while (i < 5);

A {{jsxref("Statements/while", "while")}} statement executes its statements as long as a

specified condition evaluates to `true`. A `while` statement looks

as follows:

If the `condition` becomes `false`,

`statement` within the loop stops executing and control passes to the

statement following the loop.

The condition test occurs _before_ `statement` in the loop is

executed. If the condition returns `true`, `statement` is executed

and the `condition` is tested again. If the condition returns

`false`, execution stops, and control is passed to the statement following

`while`.

To execute multiple statements, use a block statement (`{ }`) to group

those statements.

The following `while` loop iterates as long as `n` is

less than `3`:

let n = 0;

let x = 0;

while (n < 3) {

n++;

x += n;

}

With each iteration, the loop increments `n` and adds that value to

`x`. Therefore, `x` and `n` take on the following

values:

- After the first pass: `n` = `1` and `x` =

`1`

- After the second pass: `n` = `2` and `x` =

`3`

- After the third pass: `n` = `3` and `x` =

`6`

After completing the third pass, the condition `n < 3` is no longer

`true`, so the loop terminates.

Avoid infinite loops. Make sure the condition in a loop eventually becomes

`false`—otherwise, the loop will never terminate! The statements in the

following `while` loop execute forever because the condition never becomes

`false`:

```js example-bad

while (true) {

console.log("Hello, world!");

}

A {{jsxref("Statements/label", "label")}} provides a statement with an identifier that

lets you refer to it elsewhere in your program. For example, you can use a label to

identify a loop, and then use the `break` or `continue` statements

to indicate whether a program should interrupt the loop or continue its execution.

The syntax of the labeled statement looks like the following:

The value of `label` may be any JavaScript identifier that is not a

reserved word. The `statement` that you identify with a label may be

any statement. For examples of using labeled statements, see the examples of `break` and `continue` below.

Use the {{jsxref("Statements/break", "break")}} statement to terminate a loop,

`switch`, or in conjunction with a labeled statement.

- When you use `break` without a label, it terminates the innermost

enclosing `while`, `do-while`, `for`, or

`switch` immediately and transfers control to the following statement.

- When you use `break` with a label, it terminates the specified labeled

statement.

The syntax of the `break` statement looks like this:

1. The first form of the syntax terminates the innermost enclosing loop or `switch`.

2. The second form of the syntax terminates the specified enclosing labeled statement.

The following example iterates through the elements in an array until it finds the

index of an element whose value is `theValue`:

for (let i = 0; i < a.length; i++) {

if (a[i] === theValue) {

break;

}

}

let x = 0;

let z = 0;

labelCancelLoops: while (true) {

console.log("Outer loops:", x);

x += 1;

z = 1;

while (true) {

console.log("Inner loops:", z);

z += 1;

if (z === 10 && x === 10) {

break labelCancelLoops;

} else if (z === 10) {

break;

}

}

}

The {{jsxref("Statements/continue", "continue")}} statement can be used to restart a

`while`, `do-while`, `for`, or `label`

statement.

- When you use `continue` without a label, it terminates the current

iteration of the innermost enclosing `while`, `do-while`, or

`for` statement and continues execution of the loop with the next

iteration. In contrast to the `break` statement, `continue` does

not terminate the execution of the loop entirely. In a `while` loop, it

jumps back to the condition. In a `for` loop, it jumps to the

`increment-expression`.

- When you use `continue` with a label, it applies to the looping statement

identified with that label.

The syntax of the `continue` statement looks like the following:

The following example shows a `while` loop with a `continue`

statement that executes when the value of `i` is `3`. Thus,

`n` takes on the values `1`, `3`, `7`, and

`12`.

let i = 0;

let n = 0;

while (i < 5) {

i++;

if (i === 3) {

continue;

}

n += i;

console.log(n);

}

If you comment out the `continue;`, the loop would run till the end and you would see `1,3,6,10,15`.

A statement labeled `checkIandJ` contains a statement labeled

`checkJ`. If `continue` is encountered, the program

terminates the current iteration of `checkJ` and begins the next

iteration. Each time `continue` is encountered, `checkJ`

reiterates until its condition returns `false`. When `false` is

returned, the remainder of the `checkIandJ` statement is completed,

and `checkIandJ` reiterates until its condition returns

`false`. When `false` is returned, the program continues at the

statement following `checkIandJ`.

If `continue` had a label of `checkIandJ`, the program

would continue at the top of the `checkIandJ` statement.

let i = 0;

let j = 10;

checkIandJ: while (i < 4) {

console.log(i);

i += 1;

checkJ: while (j > 4) {

console.log(j);

j -= 1;

if (j % 2 === 0) {

continue;

}

console.log(j, "is odd.");

}

console.log("i =", i);

console.log("j =", j);

}

The {{jsxref("Statements/for...in", "for...in")}} statement iterates a specified

variable over all the enumerable properties of an object. For each distinct property,

JavaScript executes the specified statements. A `for...in` statement looks as

follows:

The following function takes as its argument an object and the object's name. It then

iterates over all the object's properties and returns a string that lists the property

names and their values.

function dumpProps(obj, objName) {

let result = "";

for (const i in obj) {

result += `${objName}.${i} = ${obj[i]}<br>`;

}

result += "<hr>";

return result;

}

For an object `car` with properties `make` and `model`, `result` would be:

Although it may be tempting to use this as a way to iterate over {{jsxref("Array")}}

elements, the `for...in` statement will return the name of your user-defined

properties in addition to the numeric indexes.

Therefore, it is better to use a traditional {{jsxref("Statements/for", "for")}} loop

with a numeric index when iterating over arrays, because the `for...in`

statement iterates over user-defined properties in addition to the array elements, if

you modify the Array object (such as adding custom properties or methods).

The {{jsxref("Statements/for...of", "for...of")}} statement creates a loop Iterating

over [iterable objects](/en-US/docs/Web/JavaScript/Reference/Iteration_protocols) (including

{{jsxref("Array")}}, {{jsxref("Map")}}, {{jsxref("Set")}},

{{jsxref("Functions/arguments", "arguments")}} object and so on), invoking a custom

iteration hook with statements to be executed for the value of each distinct property.

The following example shows the difference between a `for...of` loop and a

{{jsxref("Statements/for...in", "for...in")}} loop. While `for...in` iterates

over property names, `for...of` iterates over property values:

const arr = [3, 5, 7];

arr.foo = "hello";

for (const i in arr) {

console.log(i);

}

for (const i of arr) {

console.log(i);

}

The `for...of` and `for...in` statements can also be used with [destructuring](/en-US/docs/Web/JavaScript/Reference/Operators/Destructuring). For example, you can simultaneously loop over the keys and values of an object using {{jsxref("Object.entries()")}}.

const obj = { foo: 1, bar: 2 };

for (const [key, val] of Object.entries(obj)) {

console.log(key, val);

}

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