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The WeakSet object lets you store weakly held objects in a collection.

Syntax

 new WeakSet([iterable]);

Parameters

iterable
If an iterable object is passed, all of its elements will be added to the new WeakSet. null is treated as undefined.

Examples

Using the WeakSet object

var ws = new WeakSet();
var obj = {};
var foo = {};

ws.add(window);
ws.add(obj);

ws.has(window); // true
ws.has(foo);    // false, foo has not been added to the set

ws.delete(window); // removes window from the set
ws.has(window);    // false, window has been removed

Description

WeakSet objects are collections of objects. An object in the WeakSet may only occur once; it is unique in the WeakSet's collection.

The main differences to the Set object are:

  • In contrast to Sets, WeakSets are collections of objects only and not of arbitrary values of any type.
  • The WeakSet is weak: References to objects in the collection are held weakly. If there is no other reference to an object stored in the WeakSet, they can be garbage collected. That also means that there is no list of current objects stored in the collection. WeakSets are not enumerable.

Properties

WeakSet.length
The value of the length property is 0.
WeakSet.prototype
Represents the prototype for the Set constructor. Allows the addition of properties to all WeakSet objects.

WeakSet instances

All WeakSet instances inherit from WeakSet.prototype.

Properties

WeakSet.prototype.constructor
Returns the function that created an instance's prototype. This is the WeakSet function by default.

Methods

WeakSet.prototype.add(value)
Appends a new object with the given value to the WeakSet object.
WeakSet.prototype.delete(value)
Removes the element associated to the value. WeakSet.prototype.has(value) will return false afterwards.
WeakSet.prototype.has(value)
Returns a boolean asserting whether an element is present with the given value in the WeakSet object or not.
WeakSet.prototype.clear()
Removes all elements from the WeakSet object.

Specifications

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

Browser compatibility

FeatureChromeEdgeFirefoxInternet ExplorerOperaSafari
Basic support361234 No239
new WeakSet(iterable)381234 No259
new WeakSet(null) Yes1237 No ?9
add36 Yes34 No239
clear36 — 43 No34 — 46 No25 — 30 No
delete36 Yes34 No239
has36 Yes34 No239
prototype36 Yes34 No239
FeatureAndroid webviewChrome for AndroidEdge mobileFirefox for AndroidIE mobileOpera AndroidiOS Safari
Basic support36361234 No239
new WeakSet(iterable)38381234 No259
new WeakSet(null) Yes Yes1237 No ?9
add3636 Yes34 No239
clear36 — 4336 — 43 No34 — 46 No25 — 30 No
delete3636 Yes34 No239
has3636 Yes34 No239
prototype3636 Yes34 No239

See also

Document Tags and Contributors

 Last updated by: chrisdavidmills,