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




Required. The object to add to the WeakSet collection.

Return value

The WeakSet object.

Using the add method

var ws = new WeakSet();

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

ws.has(window); // true

// Weakset only takes objects as arguments
// results in "TypeError: Invalid value used in weak set" in Chrome
// and "TypeError: 1 is not a non-null object" in Firefox


Specification Status Comment
ECMAScript 2015 (6th Edition, ECMA-262)
The definition of 'WeakSet.prototype.add' in that specification.
Standard Initial definition.
ECMAScript Latest Draft (ECMA-262)
The definition of 'WeakSet.prototype.add' in that specification.

Browser compatibility

Feature Chrome Edge Firefox (Gecko) Internet Explorer Opera Safari
Basic support 36 (Yes) 34 (34) No support 23 No support
Feature Android Edge Firefox Mobile (Gecko) IE Mobile Opera Mobile Safari Mobile
Basic support No support (Yes) 34.0 (34) No support No support No support

See also

Document Tags and Contributors

 Last updated by: jameshkramer,