weak key

@nick/is/weak-key

isWeakKey

Signature

function isWeakKey(it: unknown): it is WeakKey;

Checks if a value is valid as a weak key, meaning it can be used as a key in a WeakMap, a value in a WeakSet, or as the target of a WeakRef. Weak keys can also be used as the "unregister token" argument in both the register and unregister methods of the FinalizationRegistry API.

This always includes non-null objects, arrays, and functions. Since ES2023+ it also includes symbols that are not globally registered via Symbol.for.

Parameters

Name	Info
it	The value you check.

Returns

true if it is a valid WeakKey, otherwise false.

Category

Weak Collections

See Also

• https://mdn.io/WeakMap for more information on WeakMap and weak keys.

Examples

import { isWeakKey } from "jsr:@nick/is/weak-key";

// objects and functions are always valid weak keys:
console.log(isWeakKey({})); // true
console.log(isWeakKey(() => {})); // true

// starting in ES2023+, symbols are also valid weak keys:
console.log(isWeakKey(Symbol("a"))); // true
console.log(isWeakKey(Symbol.iterator)); // true

// however, globally registered symbols are not:
console.log(isWeakKey(Symbol.for("a"))); // false

// primitives are never valid weak keys:
console.log(isWeakKey(1)); // false
console.log(isWeakKey("a")); // false

WeakKey

Signature

export type WeakKey = WeakKeyTypes[keyof WeakKeyTypes];

A value that can be used as a key in a WeakMap, a value in a WeakSet, or as the target of a WeakRef. Weak keys can also be used as the "unregister token" argument in both the register and unregister methods of the FinalizationRegistry API.

This always includes non-null objects, arrays, and functions. Since ES2023+ it also includes symbols that are not globally registered via Symbol.for.

Category

Weak Collections

Tags

WeakKey

See Also

• https://mdn.io/WeakMap for more information on WeakMap and weak keys.

WeakKeyTypes

The types that can be used as a weak key.

Category

Weak Collections

Properties

object

object: object;

symbol

symbol: symbol;

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