there you go
```
console.log([7, 4, 6, 7, 12].findIndex((_, i, a) =>
isPrime(a[a.length-1-i]))); // 3
```

Le mer. 18 juil. 2018 à 11:17, Dmitry Shulgin <shulhindvst at gmail.com> a
écrit :

>
> ---------- Forwarded message ----------
> From: Dmitry Shulgin <shulhindvst at gmail.com>
> Date: 2018-07-05 10:36 GMT+03:00
> Subject: Feature proposal
> To: es-discuss at mozilla.org
>
>
> I came across a task of finding an index of the last element in array that
> satisfies the condition, so i reversed array and found it by *findIndex *
> function.
> I was thinking:
> Why do we have *findIndex*` method, but no *findLastIndex*?
> It seems logical to follow *[index|lastIndex]Of* pair, doesn't it?
> Reversing array in this case seems too complicated to me.
>
> So, i would like to suggest new method like
> *Array.prototype.findLastIndex()*
>
> Example:
>
> function isPrime(element, index, array) {
>   var start = 2;
>   while (start <= Math.sqrt(element)) {
>     if (element % start++ < 1) {
>       return false;
>     }
>   }
>   return element > 1;
> }
>
> console.log([4, 6, 8, 12].findIndex(isPrime)); // -1, not found
> console.log([7, 4, 6, 7, 12].findIndexLast(isPrime)); // 3
>
>
> Would be glad to implement, if it makes sense.
>
> Thx for replies.
>
> P.S. Small issue on GitHub was closed due to offtop (not an issue, as i
> understand).
> https://github.com/tc39/ecma262/issues/1253
>
> _______________________________________________
> es-discuss mailing list
> es-discuss at mozilla.org
> https://mail.mozilla.org/listinfo/es-discuss
>
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there you go
```
console.log([7, 4, 6, 7, 12].findIndex((_, i, a) => isPrime(a[a.length-1-i]))); // 3
```

Le mer. 18 juil. 2018 à 11:17, Dmitry Shulgin <shulhindvst at gmail.com> a
écrit :