Why You Should Always Use === and Other Bad Practices

Re:Why You Should Always Use === and Other Bad Practices by robryk on Sunday February 09, 2014 @07:03PM (#7208139)

I've expected the JS interpreter to optimize that out. Turns out I was wrong and the version from the article is even 40% slower for a loop that iterates over 5000 elements and does a trivial amount of work:

http://jsperf.com/for-loop-vs-for-in-loop/18

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Re:Why You Should Always Use === and Other Bad Practices by inglor on Sunday February 09, 2014 @07:09PM (#7208168)

You're not giving the JIT a chance to warm up at all. Also, you're degrading into 'slow mode' because your array has different types. Basically, it looks like you're doing a lot of bad things to the JIT on purpose :P

Both the different types and the delete (array with holes) are _very_ harmful for performance in v8.

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Re:Why You Should Always Use === and Other Bad Practices by goldenkey on Monday February 10, 2014 @02:19AM (#7209612)

The arrays with holes are called Sparse Arrays, I googled for 'sparse array v8 performance' and didn't find much, but I've previously seen a Google Presentation on a slide-sharing site that did mention how poor sparse arrays perform when compared to normal contiguous arrays.

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