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WeakMap.prototype.has() - JavaScript | MDN
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WeakMap.prototype.has()
Baseline
Widely available
This feature is well established and works across many devices and browser versions. It’s been available across browsers since July 2015.
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
js
has(key)
Parameters
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()
js
const wm = new WeakMap();
wm.set(window, "foo");
wm.has(window); // returns true
wm.has("baz"); // returns false
Specifications
| Specification |
|---|
| ECMAScript® 2026 Language Specification # sec-weakmap.prototype.has |
Browser compatibility
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