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.
Syntax
keys()
Parameters
None.
Return value
A new iterable iterator object.
Examples
Using keys()
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); // {}