[moosingin3space]

The problem with this is that it generates two intermediate arrays in the maps, then effectively drops them in the reduce. This may be inefficient.

I wish that JavaScript's map/filter/reduce functions returned lazy iterators, like in Rust, so that code like this doesn't produce intermediate arrays. Does anyone know of a library that provides this?

[marmart]

Those intermediate iterations could be dropped by composing the map functions together (same with the reduce), if that really was a performance bottleneck.

[moosingin3space]

With lazy iterators, there is the possibility of better composition of maps/filters/reduces. That's why I'm a fan of the lazy iterators approach -- otherwise the abstraction breaks too easily and it ends up looking like a for-loop anyway.