ECMAScript feature suggestion: Streaming Array items through filter/map/reduce functions

Oliver Dunk oliver at
Fri Jun 21 20:58:18 UTC 2019

This seems like a good place to share the idea, and it’s helpful that you provided use cases etc.

Is there a reason why you prefer the proposed syntax over the forEach loop you mentioned? Personally I like how the forEach is easy to understand, but maybe there are other examples of when the stream is useful and the polyfill is much more complex.

> On 21 Jun 2019, at 16:32, Roma Bronstein <outsidenote at> wrote:
> Hi,
> It's my first time suggesting a feature, hope I'm doing it correctly.
> I really like using, Array.prototype.reduce() and all related functions.
> The code is more readable and it looks better.
> However, when I want to write performance sensitive code, chaining these functions is not a good approach.
> For example, writing this:
> // a is an Array of length N
> const b = a.filter().map()
> will require 2 traversals over the whole array, up to 2*N iterations (if the filter passes all items).
> This is why I often resort to writing this:
> const b= []
> a.forEach(() => {
>   if (/*the filter condition*/)
>     b.push(/*mapping logic*/)
> })
> Which requires only N iterations.
> I suggest adding a capability to streamline items to these functions.
> I get my inspiration from Redis's transaction syntax where you declare starting a transaction and finally call EXEC in order to execute it.
> So now I'll be able to write something like this:
> const b =
>   .filter()
>   .map()
>   .exec()
> Just to clarify the example:
> I've declared that I'd like to stream array items of a. Then I've chained the functions I'd like to items to pass through.
> Finally I've activated it using the exec() function.
> I'm not sure if this is the best syntactical approach, but this example is more intuitive to understand in my opinion.
> Another approach could be thinking about a "pipeline" operator like in UNIX cli, providing a more generic capability to pipeline iterators.
> Again, I hope I'm doing this correctly and in the right forum.
> And if so, I'd be happy to hear some feedback.
> Thanks,
> Roma
> _______________________________________________
> es-discuss mailing list
> es-discuss at

More information about the es-discuss mailing list