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colinhackscolinhacks
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feat(instanceof): key the .properties() shape off the instance type (#6600)
The method took any $ZodShape, so a misspelled key or a schema that can't accept the property's type both compiled. The shape is now a mapped type over keyof T, which also makes the keys autocomplete. Methods are excluded from the shape. Every object literal inherits Object.prototype.toString, so a constraint carrying URL's own toString entry rejects every shape literal passed to it. Type-only: the emitted JS is byte-identical, so runtime, memory and bundle are all unchanged.
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Lines changed: 21 additions & 1 deletion

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‎packages/zod/src/v4/classic/schemas.ts‎

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@@ -2841,7 +2841,8 @@ type ZodInstanceOfParams = core.Params<
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// ZodInstanceOf
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export interface ZodInstanceOf<T = unknown> extends ZodCustom<T, T> {
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properties<Shape extends core.$ZodShape>(
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// the shape is keyed off the instance type, so keys autocomplete and a schema that can't accept the property's type is an error. Methods are excluded: every object literal inherits Object.prototype.toString, which would otherwise collide with the constraint's own toString entry and reject every shape.
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properties<Shape extends { [k in keyof T as T[k] extends Function ? never : k]?: core.$ZodType<unknown, T[k]> }>(
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shape: Shape,
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params?: string | core.$ZodCheckPropertiesParams
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): ZodInstanceOf<T & core.$InferObjectInput<Shape, {}>>;

‎packages/zod/src/v4/classic/tests/properties.test.ts‎

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@@ -51,6 +51,25 @@ test("z.instanceof().properties()", () => {
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expectTypeOf<z.infer<typeof W>>().toEqualTypeOf<URL & { search: string }>();
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});
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test("z.instanceof().properties() constrains the shape to the instance type", () => {
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const file = z.instanceof(File).properties({ name: z.string(), size: z.number().max(1024) });
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expectTypeOf<z.infer<typeof file>>().toEqualTypeOf<File & { name: string; size: number }>();
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// @ts-expect-error no such property on File
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z.instanceof(File).properties({ nmae: z.string() });
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// @ts-expect-error File["size"] is a number
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z.instanceof(File).properties({ size: z.string() });
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// methods are out of the shape, so an object literal's inherited toString can't collide with the constraint
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// @ts-expect-error
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z.instanceof(File).properties({ text: z.any() });
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// a literal still narrows a wider property
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const png = z.instanceof(File).properties({ type: z.literal("image/png") });
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expectTypeOf<z.infer<typeof png>>().toEqualTypeOf<File & { type: "image/png" }>();
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});
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test("z.properties spreads into .check()", () => {
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// the 4.5 array call sites: the check yields itself from Symbol.iterator
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const p = z.properties({ a: z.literal("x") });

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