The set() method adds a new element with a specified key and value to a WeakMap object.


wm.set(key, value);


Required. The key of the element to add to the WeakMap object.
Required. The value of the element to add to the WeakMap object.

Return value

The WeakMap object.


Using the set method

var wm = new WeakMap();
var obj = {};

// Add new elements to the WeakMap
wm.set(obj, 'foo').set(window, 'bar'); // chainable

// Update an element in the WeakMap
wm.set(obj, 'baz');


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

Browser compatibility

FeatureChromeEdgeFirefoxInternet ExplorerOperaSafari
Basic support36 Yes61112238
FeatureAndroid webviewChrome for AndroidEdge mobileFirefox for AndroidOpera AndroidiOS SafariSamsung Internet
Basic support3636 Yes61238 Yes

1. Prior to Firefox 38, this method threw a TypeError when the key parameter was not an object. This has been fixed in version 38 and later to return false as per the ES2015 standard.

2. Returns 'undefined' instead of the 'Map' object.

3. From version 0.10: this feature is behind the --harmony runtime flag.

Firefox-specific notes

  • Prior to Firefox 33 (Firefox 33 / Thunderbird 33 / SeaMonkey 2.30), WeakMap.prototype.set returned undefined and was not chainable. This has been fixed (bug 1031632). The behavior can be found in Chrome/v8 as well (issue).

See also

Document Tags and Contributors

Contributors to this page: wbamberg, fscholz, jameshkramer, nmve, kdex, realityking, ziyunfei
Last updated by: wbamberg,