Discussion on: Map, Filter, Reduce vs For Loops (syntax)

[JavaScript Joel]

I was trying to keep it simple for noobs but I think your solution is much cleaner.

Typically I will use a mutable accumulator in a reducer. Your version is immutable so every iteration will produce a new array. Not the best for performance but this is just for example anyway.

[Mesteche]

Then with a mutable accumulator :

const reducer = (filter, map) => (acc, x) =>
  (filter(x) && acc.push(map(x)), acc)

[JavaScript Joel]

Awesome!

I'm a big fan of the comma operator. I decided to leave it out in this code block to not confuse anyone. But I use it pretty regularly in my own codebase.

[John]

Hi Joel,

I'm one of those noobs, but trying my very best not to be. I am trying to teach myself functional programming in JavaScript and I have come upon the subject of transducers. This code looks very similar; can you confirm that this code is, or is closely related to the concept of transducers.

Thanks

[JavaScript Joel]

Transducers are the next evolution. You would start with a list, and learn map, filter, reduce. Once you start applying multiple map/filter/reduces to a single list, you realize you are enumerating the list multiple times, which will slow down your application.

Transducers are a way to apply those multiple map/filter/reduces while enumerating the list one time.