re: Please don't "overchain" array methods VIEW POST


This is what I call unnecessary optimization. If you follow time complexity optimization, O(3n) is still just O(n). Now, I'm not sure what the space complexity is on this, but unless your arrays are massive, I'm sure it's negligible for integers.

.map and .filter do create new arrays so that definitely is something to be aware of, but doing 3 operations in 1 loop is effectively the same thing as 3 loops with 1 operation.

I think you're misleading beginner JS developers with this article.


Yes, that is right. But even though they ultimately boil down to an O(n) time complexity, it can still have a significant performance impact if your arrays are massive, as you said. In a way, I'm not really misleading beginners here because it's the truth of the matter.

But for most cases, one does not need to worry about these performance impacts. It really is just an unnecessary optimization.


I don't believe that you make any comments about .map using more space in your article do you? You also don't comment and say this is only worth doing in one step if your arrays are massive. That's why I suggest that you are misleading beginners. Your example is contrived. For this article to be really useful, you should use a really big array as an example and demonstrate the performance benefits of moving all your operations into the reducer. At the same time, you should speak about the code using significantly less space and that's why it's faster.

Ah, I see now. There's a reason why I didn't add the #beginners tag for this article. It is exactly for the reason you stated. I wasn't targeting beginners for this article. I was assuming that those who read it will most likely know how to optimize their algorithms themselves with what they learned from this article as a guide on how to do so. I suppose that was wrong of me to assume.

Also, I was actually thinking about discussing the space inefficiency of long chains of array methods, but I felt that doing so would have caused me to stray away from the actual message I was trying to convey throughout the whole article: longer chains mean more iterations.


Waiting 1m is still better than waiting 3m. Disregarding the less significant factors in O(3n) is not always a good idea in practice.

I agree all of this is a pretty useless exercise when you have 3 consecutive maps over 10 or even 1000 items, but this optimization is the reason many FP libraries offer super easy to use pipe/compose functions.

I'd say, if the optimization is that easy, do it — even if the gains small. Without pipe/compose available, I'd be in favor of readability over performance though.


What are you talking about. The time complexity doesn't change by moving everything into the reducer, it's the space complexity that changes because .map creates a new array. It's not 1ms vs 3ms...

You are right that it doesn't take three times as long, my mistake.

But it's never just "1+1+1=3" either.

Especially if the arrays are large, and the operations are simple, then the overhead of copying the array doesn't just affect memory use, it also takes longer.


The only comment based on the O notation in both time and space complexity. Looks like not all folks know about that.

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