WeakSet.prototype.has()

Baseline Widely available

This feature is well established and works across many devices and browser versions. Its been available across browsers since September 2015.

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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

has(value)

Parameters

value: The value to test for presence in the WeakSet object. Objects are compared by reference, not by value.

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()

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);