WeakSet.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 September 2015.
The has() method of WeakSet instances returns a boolean indicating whether the specified value exists in this WeakSet or not.
Try it
const weakset = new WeakSet();
const object1 = {};
const object2 = {};
weakset.add(object1);
console.log(weakset.has(object1));
// Expected output: true
console.log(weakset.has(object2));
// Expected output: false
Syntax
js
has(value)
Parameters
Return value
Returns true if the specified value exists in the WeakSet object; otherwise false. Always returns false if value is not an object or a non-registered symbol.
Examples
Using has()
js
const ws = new WeakSet();
const obj = {};
ws.add(window);
ws.has(window); // returns true
ws.has(obj); // returns false
// Storing a non-registered symbol
const sym = Symbol("foo");
ws.add(sym);
ws.add(Symbol.iterator);
Specifications
| Specification |
|---|
| ECMAScript® 2026 Language Specification # sec-weakset.prototype.has |
Browser compatibility
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