WeakMap.prototype.set()

Baseline Widely available

This feature is well established and works across many devices and browser versions. It’s been available across browsers since July 2015.

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

Try it

const weakmap1 = new WeakMap();
const object1 = {};
const object2 = {};

weakmap1.set(object1, "foo");
weakmap1.set(object2, "bar");

console.log(weakmap1.get(object1));
// Expected output: "foo"

console.log(weakmap1.get(object2));
// Expected output: "bar"

Syntax

js
set(key, value)

Parameters

key

Must be either an object or a non-registered symbol. The key of the entry to add to the WeakMap object.

value

Any value representing the value of the entry to add to the WeakMap object.

Return value

The WeakMap object.

Exceptions

TypeError

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

Examples

Using the set() method

js
const wm = new WeakMap();
const 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");

// Using a non-registered symbol as key
const sym = Symbol("foo");
wm.set(sym, "baz");
wm.set(Symbol.iterator, "qux");

Specifications

Specification
ECMAScript® 2025 Language Specification
# sec-weakmap.prototype.set

Browser compatibility

Report problems with this compatibility data on GitHub
desktopmobileserver
Chrome
Edge
Firefox
Opera
Safari
Chrome Android
Firefox for Android
Opera Android
Safari on iOS
Samsung Internet
WebView Android
WebView on iOS
Deno
Node.js
set

Legend

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Full support
Full support
See implementation notes.

See also