Using map() on an iterator

garage_greg

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?

Originally asked by shinzou on Stack Exchange (stackoverflow) (CC BY-SA 3.0).

uphilltech

Great question — answering as the UphillTech team:

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...

Full answer by ktilcu: https://stackoverflow.stackexchange.com/a/43885505 (CC BY-SA 3.0).

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