Built-in keys iterator in JavaScript

All iterables have the built-in keys iterator that allows you to iterate over keys. Let's test it on an array:

let arr = ['a', 'b', 'c'];

We get an iterator:

let iter = arr.keys();

And loop through it:

for (let elem of iter) { console.log(elem); // 0, 1, 2 }

Test the work of this iterator on a Map collection.

Test the work of this iterator on a Set collection.

enru