[syg]

The slowness of functional methods like .map and .forEach for a time was due to their not being self-hosted. Since then, both V8 and SpiderMonkey self-host them, and bz has posted some numbers below [1].

But perf problems are more numerous still for these functional methods, because compilers in general have trouble inlining closures, especially for very polymorphic callsites like calls to the callback passed in via .map or .forEach. For an account of what's going on in SpiderMonkey, I wrote an explanation about a year ago [2]. Unfortunately, the problems still persist today.

[1] https://news.ycombinator.com/item?id=7938101 [2] http://rfrn.org/~shu/2013/03/20/two-reasons-functional-style...