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Discussion on: Don’t pay the for-loop tax

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Josh Cheek

So for N loops, you get at least N+1 additional function calls, with all of the associated overhead, compared to just having some code in a loop.

I may be wrong, but I would have assumed that modern JS interpreters can optimize this away. I would also expect it to be faster to call the loop they implement in the underlying language.

Calling map/reduce/filter doesn't eliminate the for loop, it merely moves it. The implementation of these methods has... you guessed it... a for loop.

If you're iterating over an array, but not necessarily for other iterable structures. A nice thing about using the iterator functions is that you don't have to know / care what kind of collection you're iterating over. Using the abstractions means you don't have to embed iteration knowledge at every location in your code that you want to iterate. Your code doesn't change just because the details of how to iterate change.

Loops can break or return early. While findIndex() helps with some situations you'd need that for, other use cases don't have an equivalent.

IIRC, there's an interface for defining iterators that allows them to return early.

Loops can modify their iterator variable, allowing them to skip over values (or even go back). Granted, this is an edge case.

It's a good point, if you can't do that, then you have to retain state somehow (probably via a stack). Although, if the logic for how to prepare for the next iteration were that complex, I would probably choose a while loop over a for loop (or perform the update section of the for loop in its body).