Functional programming, and it's degenerate cousin, cramming random functional constructs (array comprehension methods, willy-nilly currying, ...) in Javascript has been the worst thing to happen to web programming.

What that has done is made a whole generation of developers completely detached of the impact on heap allocation and GC. If web programs are slow and bloated, it's partly because of using nuggets from functional programming just for the sake of it.