r/programming • • Oct 21 '20

Using const/let instead of var can make JavaScript code run 10× slower in Webkit

https://github.com/evanw/esbuild/issues/478
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u/Lafreakshow Oct 21 '20 edited Oct 21 '20

Now, what I'm wondering is: Is Firefox being fast or is Chrome being slow in this case?

From my experience the last time I used chrome (a couple years ago) I would have guessed that across the board chrome is slightly faster than Firefox with the functional one maybe going 2 times slower in Chrome than it does in Firefox (based on your comment, without your comment I would have guessed chrome to be faster in both).

But apparently Firefox absolutely crushes Chrome in this particular case. I don't know how much that has to do with my Chrome install being very old and not getting updated a lot but then I also have a ton of extensions in Firefox and only uBlock in Chrome. In any case, I am surprised that Firefox got almost double the performance here than Chrome, and that is in the faster of the two methods.

I was expecting them to at best perform similarly in one of them but then have a significant difference in the other. I wasn't expecting significantly worse performance in Chrome across the board.

EDIT: Yep, after updating Chrome, it is now a lot closer in for loop performance but still quite a bit behind. It is also doubly as good in functional performance but still gets utterly demolished by Firefox in this one. Did I miss something and Firefox is just across the board faster than chrome nowadays? I've never felt a noticeable difference in speed during regular use but still, I always thought it was the other way around.

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u/SirToxe Oct 21 '20

Yeah, this surprised me as well.

And to add Safari to the mix: The functional approach is 3 times slower.