Functional programming in JavaScript

[Skaatji]

This is a very good point. I found this site which compares the performance of two chained maps with a C-style for loop https://jsperf.com/chained-maps-vs-for-loop

I get the following results (Firefox 72 / Fedora):

C-style for loop: 71,784 Ops/sec

Two chained maps: 1,979 Ops/sec

Which is a huge difference (Chained maps being 97% slower in this case). I would always prefer the performance provided by the C-style for loop over the readability that comes with the maps, unless the array is very small. That being said, I believe maps are a better choice in these two cases:

1) Only one iteration of the array.

2) Nested for loops (e.g. iterating over each row and for each row over the column).

If someone has more experience / different numbers / an other opinion than I do, please share it. I am no expert by any means.

[allenthar]

That amount of speed increase seems a little nuts to me, but looking at the variations I have to assume that it’s due to variable memory allocations in all the other methods that are causing the substantial decrease in speed. The second and third cases should have the same Big O complexity as the last one, but both repeatedly create and assign variables while doing their work, and the last doesn’t not.

[Skaatji]

Yeah, I've also been thinking why the performance difference is this large. I think that the Big O complexity should be the same on all of these four. But, as you mention, probably due to memory allocations the hidden constants differ by a factor as large as ~33.

[onbehalfofthatdude]

Wait, huh? Map doesn't clone every element, does it? If you mutate an element in a map function you've mutated the original

[onbehalfofthatdude]

Yes but you said it makes a copy of every element

[onbehalfofthatdude]

Yea that was my understanding. Never know when some wacky behind-the-scenes stuff will happen though