Map.prototype.keys()

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

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); // {}