[thomasfoster96]

forEach is awfully slow compared to a for statement if you're dealing with numbers - less so with strings/objects, but it's still noticeable (like 10x whenever I've tested it at best).

Caching the array length still gives you a small speed boost in most browsers, but it's probably an over optimisation unless you're doing something really intensive.

[pluma]

If you're doing number crunching, yes, don't use forEach.

If you're just writing ordinary business code (i.e. in 80% of all code out there), by all means, please use forEach and friends.

Besides, if you're doing number crunching in JS, you probably want to stick to ASM.js anyway.

[jaredsohn]

I think a big reason to cache the array length within interviews (for cases when it isn't already cached) is that to not do so can often increase the complexity of a solution by a factor of O(n).