[rakoo]

> The problem with this is to be able to add a custom function to this pipeline, you have to extend the prototype of the library with your own functions, or re-implement it.

That's exactly what transducers try to solve, and fortunately they do exist for js (http://jlongster.com/Transducers.js--A-JavaScript-Library-fo...) where processing of individual elements is separated from plumbing, so you can add your own custom computation in the chain. It even has pretty good performances (http://jlongster.com/Transducers.js-Round-2-with-Benchmarks), all with the standard data structures !

Of course transducers are useful only when you want to transform data, not when you want to act on them in the chain.