WeakSet.prototype.add()

The add() method of WeakSet instances appends a new object to the end of this WeakSet.

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Syntax

js
add(value)

Parameters

value

Must be either an object or a non-registered symbol. The value to add to the WeakSet collection.

Return value

The WeakSet object.

Exceptions

TypeError

Thrown if value is not an object or a non-registered symbol.

Examples

Using add

js
const ws = new WeakSet();

ws.add(window); // add the window object to the WeakSet

ws.has(window); // true

// WeakSet only takes objects as arguments
ws.add(1);
// results in "TypeError: Invalid value used in weak set" in Chrome
// and "TypeError: 1 is not a non-null object" in Firefox

Specifications

Specification
ECMAScript Language Specification
# sec-weakset.prototype.add

Browser compatibility

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See also