On Wed, Oct 1, 2014 at 2:50 PM, Dmitry Soshnikov <dmitry.soshnikov at gmail.com
> wrote:

> Hi,
>
> (Maps are awesome!)
>
> 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.
>


Only with regard to time. I expect there will be substantial additions to
Map and Set in ES7 (as long as the work is done, of course).


>
> 2. Declarative syntax
>
> The other thing to note: currently maps a lack of a nice declarative
> syntax. This one came from the use-case for maps for dynamic (computed)
> property names.
>

> Previously, we had to allocate an empty object, and then, in the
> imperative style, append needed props:
>
> ```
> var requestData = {};
> requestData[Names.ID] = id;
> requestData[Names.EMAIL] = email;
> requestData.needsReload = true;
> ...
> new Request(...)
>   .setData(requestData)
>   .send();
> ```
>
> With computed properties of object initialisers it's much simpler and
> convenient:
>
> ```
> new Request(...)
>   .setData({
>     [Names.ID]: id,
>     [Names.EMAIL]: email,
>     needsReload: true,
>   })
>   .send();
> ```
>
> Then thing is: if we'd like to use maps for such use-case, it brings us
> back to that inconvenient imperative style of assignments (even worse,
> since you have to repeat that `.set(...)` constantly):
>
> ```
> var requestData = new Map();
> requestData.set(Names.ID, id);
> requestData.set(Names.EMAIL, email);
> requestData.set('needsReload', id);
> ...
> ```
>
> Yes, we provide the iterable option for the constructor, and it can be
> rewritten as (and this can even be inlined):
>
> ```
> var requestData = new Map([
>   [Names.ID, id],
>   [Names.EMAIL, email],
>   ['needsReload', id]
> ]);
> ```
>
> However, obviously, it's too many arrays allocation for such a simple use
> case.
>
> Will it make sense having a nice declarative syntax like:
>
> ```
> new Map({
>   [Names.ID]: id,
>   [Names.EMAIL]: email,
>   needsReload: true,
> })
> ```
>

This doesn't work because Maps allow objects as keys.

Rick
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> Was it an intended decision not to have `Map#map`, `Map#filter`?

Only with regard to time. I expect there will be substantial additions to
Map and Set in ES7 (as long as the work is done, of course).

> Will it make sense having a nice declarative syntax like:
>
> ```js
> new Map({
>   [Names.ID]: id,
>   [Names.EMAIL]: email,
>   needsReload: true,
> })
> ```

This doesn't work because Maps allow objects as keys.