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Discussion on: Stop mutating in map, reduce and forEach

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marcosvega91 profile image
Marco Moretti • Edited

Both examples are O(n) complexity so they should be almost similar. Only on large example you will see differences

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smeijer profile image
Stephan Meijer Author

True. I can't believe I missed that. Jacob Paris explains it dead simple in a tweet.

Looping once and doing three things on each item performs the same as doing one thing on each item but looping three times.

It's time I return to school.

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hiasltiasl profile image
Matthias Perktold

I also expected the filter+map version to be slower, not because of the extra loop, but because of the intermediate array that needs to be created. But maybe the browser can optimize it away.

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smeijer profile image
Stephan Meijer Author

I haven't profiled it on that level, so maybe there is a difference in memory usage. I honestly don't know. Browsers have changed quite a bit over the last few years. So I wouldn't be surprised if the intermediate array has been optimized away.

It would be interesting to compare the memory profiles though.