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 entry with a specified key and value to this WeakMap, or updates an existing entry if the key already exists.

Try it

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

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

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

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

Syntax

set(key, value)

Parameters

key

The key of the entry to add to or modify within the WeakMap object. Must be either an object or a non-registered symbol. Object keys are compared by reference, not by value.

value

The value of the entry to add to or modify within the WeakMap object. Can be any value.

Return value

The WeakMap object.

Exceptions

TypeError

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

Examples

Using set()

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");