WeakMap.prototype.has()

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

{{InteractiveExample("JavaScript Demo: WeakMap.prototype.has()")}}

```js interactive-example 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

```js-nolint
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#

{{Specifications}}

Browser compatibility#

{{Compat}}

See also#

• {{jsxref("WeakMap")}}
• {{jsxref("WeakMap.prototype.delete()")}}
• {{jsxref("WeakMap.prototype.get()")}}
• {{jsxref("WeakMap.prototype.set()")}}