Add support for Iterator Helpers (now stage 3)

[thesoftwarephilosopher]

⚙ Compilation target

ESNext

⚙ Library

n/a

Missing / Incorrect Definition

IterableIterator should have map/filter/etc.

Sample Code

// Tested in both Node 22 and latest Edge

const m = new Map([[1, 2], [3, 4]]);
const keys = m.keys(); // IterableIterator<number>
const iter = keys.map(n => n * 100);
// Property 'map' does not exist on type 'IterableIterator<number>'.ts(2339)

const val = iter.next();
console.log(val);
// {value: 100, done: false}

Documentation Link

• https://github.com/tc39/proposal-iterator-helpers
• https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Iterator/map
• https://caniuse.com/?search=JavaScript%20built-in%3A%20Iterator%3A%20map

[xiBread]

Already added in #58222

[jakebailey]

Yep: https://devblogs.microsoft.com/typescript/announcing-typescript-5-6-beta/#iterator-helper-methods

Playground Link

[thesoftwarephilosopher]

Ah I thought I saw this somewhere. Thanks guys.

[thesoftwarephilosopher]

Why do those docs say

and for some reason reduce

? Like, is reduce known to be useless in lazy iterators or something?

[RyanCavanaugh]

I have no idea lol. @DanielRosenwasser ?

[DanielRosenwasser]

It was just a playful dig at the method. reduce can be useful but unfortunately I find most uses of it are super inefficient, are just a bad forEach, or overly clever. You can feel free to use reduce and I won't judge you. 😄

[thesoftwarephilosopher]

True, come to think of it, I can't remember how many years it's been since I actually used reduce.