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


 new WeakSet([iterable]);


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


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.


The value of the length property is 0.
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.


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


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


Using the WeakSet object

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


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


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) (Yes)1237 No ?9
add36 (Yes)34 No239
clear36 — 43 No34 — 46 No25 — 30 No
delete36 (Yes)34 No239
has36 (Yes)34 No239
prototype36 (Yes)34 No239
FeatureAndroidChrome for AndroidEdge mobileFirefox for AndroidIE mobileOpera AndroidiOS Safari
Basic Support36361234 No239
new WeakSet(iterable)38381234 No259
new WeakSet(null) (Yes) (Yes)1237 No ?9
add3636 (Yes)34 No239
clear36 — 4336 — 43 No34 — 46 No25 — 30 No
delete3636 (Yes)34 No239
has3636 (Yes)34 No239
prototype3636 (Yes)34 No239

See also

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