Using map() on an iterator

Question

Say we have a Map: let m = new Map();, using m.values() returns a map iterator.

But I can't use forEach() or map() on that iterator and implementing a while loop on that iterator seems like an anti-pattern since ES6 offer functions like map().

So is there a way to use map() on an iterator?

Answer 1

The simplest and least performant way to do this is:

Array.from(m).map(([key,value]) => /* whatever */)

Better yet

Array.from(m, ([key, value]) => /* whatever */))

Array.from takes any iterable or array-like thing and converts it into an array! As Daniel points out in the comments, we can add a mapping function to the conversion to remove an iteration and subsequently an intermediate array.

Using Array.from will move your performance from O(1) to O(n) as @hraban points out in the comments. Since m is a Map, and they can't be infinite, we don't have to worry about an infinite sequence. For most instances, this will suffice.

There are a couple of other ways to loop through a map.

Using forEach

m.forEach((value,key) => /* stuff */ )

Using for..of

var myMap = new Map();
myMap.set(0, 'zero');
myMap.set(1, 'one');
for (var [key, value] of myMap) {
  console.log(key + ' = ' + value);
}
// 0 = zero
// 1 = one