The has() method of WeakMap instances returns a boolean indicating whether an entry with the specified key exists in this WeakMap or not.

Try it

const weakmap = new WeakMap();
const object1 = {};
const object2 = {};

weakmap.set(object1, "foo");

console.log(weakmap.has(object1));
// Expected output: true

console.log(weakmap.has(object2));
// Expected output: false

Syntax

has(key)

Parameters

key

The key of the entry to test for presence in the WeakMap object. Object keys are compared by reference, not by value.

Return value

Returns true if an entry with the specified key exists in the WeakMap object; otherwise false. Always returns false if key is not an object or a non-registered symbol.

Examples

Using has()

const wm = new WeakMap();
wm.set(window, "foo");

wm.has(window); // returns true
wm.has("baz"); // returns false

Specifications

Browser compatibility

See also

• WeakMap
• WeakMap.prototype.delete()
• WeakMap.prototype.get()
• WeakMap.prototype.set()