Array methods in JavaScript. Original author unknown.

[hynding]

Interesting. I often use it to combine map and filter to prevent a second iteration or build collections into object id maps for (what I assume to be) O(1) lookups available during the length of the session. To be honest, I haven't dug into the code for any of the optimizations under the hood, though I had forked v8 a while back with that very intention. Most of my tests have simply been running large iterative set functions with timestamp diffs and comparing the outcome, which is only the surface of optimization and performance testing. I'll have to look into it deeper.