> 1. Transforming iteration methods
> 
> We're currently polyfillying the `Map`, and got some questions form devs. One of them is about transforming iteration methods, like `map` and `filter`.
> 
> Unfortunately I missed that part of the spec when it was approved, so can someone please remind/clarify -- was it an intended decision not to hap Map#map, Map#filter? I can see only Map#forEach in the spec. Are maps "immutable"? -- That's fine, the `map` and `filter` return a new map.


FWIW: I’ll probably use the following work-arounds. I don’t expect performance to be an issue for my applications; it’d be interesting to hear if it becomes a problem for someone.

```js
let map2 = new Map(map1.entries().filter((key, value) => key >= 0));
let map2 = new Map(map1.entries().map((key, value) => [key * 2, value * 2]));
```

-- 
Dr. Axel Rauschmayer
axel at rauschma.de
rauschma.de



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FWIW: I’ll probably use the following work-arounds. I don’t expect performance to be an issue for my applications; it’d be interesting to hear if it becomes a problem for someone.

```js
let map2 = new Map(map1.entries().filter((key, value) => key >= 0));

let map2 = new Map(map1.entries().map((key, value) => [key * 2, value * 2]));
```