WeakSet.prototype.has()

The has() method of WeakSet instances returns a boolean indicating whether an object exists in this WeakSet or not.

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Syntax

js
has(value)

Parameters

value

The value to test for presence in the WeakSet.

Return value

Returns true if an element with 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 the has() method

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 Language Specification
# sec-weakset.prototype.has

Browser compatibility

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See also