for statement with index and value

[Rick Waldron]

If you need the _index of_ a value in an array, there is always...
"indexOf" ;)

for (let value of values) {
  let index = values.indexOf(value);
}

Rick

On Tue, Jul 14, 2015 at 4:16 PM Tab Atkins Jr. <jackalmage at gmail.com> wrote:

> On Mon, Jul 13, 2015 at 7:13 PM, Tingan Ho <tingan87 at gmail.com> wrote:
> > Just following a discussion we had on TypeScript
> > https://github.com/Microsoft/TypeScript/issues/3835
> >
> > In most times, I just need the value in an array, so I use a for..of
> loop.
> > But then, I find out that I need the index too, then I need to rewrite my
> > whole for loop expression. Happens all the time for me.
> >
> > I have to ask why there doesn't exist a `for statement` where I can get
> the
> > index and value of an array directly? Or for that matter property and
> value
> > of an object?
> >
> > `.forEach` is not ideal since you can't break, break to outer loop and
> > continue cleanly. Even though you can achieve this with other array
> methods,
> > I don't think they are as productive as a for-statement.
> >
> > What I'm suggesting is augmenting the current syntax for `for..of` loops.
> > And support an overloading pattern so that we don't need to rewrite the
> > whole for loop expression to just to get the index when we already
> getting
> > the value.
> >
> > ```
> > // overloads
> > for (let value, index of values) { ... }
> > for (let value of values) { ... }
> > ```
> >
> > PS. Sorry if this has already discussed. Couldn't find any on Google and
> the
> > esdiscuss.org page doesn't have any search capabilities.
>
> Kevin provided the built-in answer for arrays, but for arbitrary
> iterables, the Python solution is trivial:
>
> function* enumerate(iter) {
>   let i = 0;
>   for(let value of iter) {
>     yield [i, value];
>     i++
>   }
> }
>
> for(let [i, v] of enumerate(values)) {
>   ...
> }
>
> I expect there's already libraries that duplicate all of Python's
> itertools and more; the iterator algebra is really trivially hackable.
>
> ~TJ
> _______________________________________________
> es-discuss mailing list
> es-discuss at mozilla.org
> https://mail.mozilla.org/listinfo/es-discuss
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mail.mozilla.org/pipermail/es-discuss/attachments/20150715/9ea918cb/attachment.html>