JS: Map.prototype.keys

By Xah Lee. Date: . Last updated: .

(new in ECMAScript 2015)

mapObj.keys()

Return a Generator for the keys in the map.

const mm = new Map([[3, "n3"], [4, "n4"]]);
for (let k of mm.keys()) {
 console.log(k);
}
// 3
// 4

Verify Result is a Generator

// verify the result is iterator and iterable

const xx = (new Map([[1, 2], [3, 4]])).keys();

// is iterable
console.log(Reflect.has(xx, Symbol.iterator));
// true

// is iterator
console.log(Reflect.has(xx, "next"));
// true