Map.prototype.has()
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 has() method of WeakMap instances returns a boolean indicating whether an entry with the specified key exists in this WeakMap or not.
Try it
const map = new Map();
map.set("bar", "foo");
console.log(map.has("bar"));
// Expected output: true
console.log(map.has("baz"));
// Expected output: false
Syntax
js
has(key)
Parameters
Return value
Returns true if an entry with the specified key exists in the Map object; otherwise false.
Examples
Using has()
js
const myMap = new Map();
myMap.set("bar", "foo");
console.log(myMap.has("bar")); // true
console.log(myMap.has("baz")); // false
Specifications
| Specification |
|---|
| ECMAScript® 2026 Language Specification # sec-map.prototype.has |
Browser compatibility
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