Map.prototype.keys()
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 keys() method of Map instances returns a new map iterator object that contains the keys for each element in this map in insertion order.
Try it
const map = new Map();
map.set("0", "foo");
map.set(1, "bar");
const iterator = map.keys();
console.log(iterator.next().value);
// Expected output: "0"
console.log(iterator.next().value);
// Expected output: 1
Syntax
js
keys()
Parameters
None.
Return value
A new iterable iterator object.
Examples
Using keys()
js
const myMap = new Map();
myMap.set("0", "foo");
myMap.set(1, "bar");
myMap.set({}, "baz");
const mapIter = myMap.keys();
console.log(mapIter.next().value); // "0"
console.log(mapIter.next().value); // 1
console.log(mapIter.next().value); // {}
Specifications
| Specification |
|---|
| ECMAScript® 2027 Language Specification # sec-map.prototype.keys |