No, because accessing a object property requires a hash table lookup.

brown9-2 · on Nov 12, 2009

But just stating why a more performant option exists doesn't tell us how much performance you'll squeeze out just by making this change.

In other words, it's not very helpful to say "this is so slow, you should do this instead" without at least trying to quantify the difference somehow.

asher · on Nov 12, 2009

I just tried it.

With 10M entries in the array, the "slow" way takes 509 ms and the "faster" way takes 362 ms. So we can save roughly 15 nanoseconds per iteration. Or a 30% speedup - assuming nothing happens inside the loop.

(Of course the numbers may vary wildly per browser.)

Somehow I doubt this is the performance problem behind slow web pages.

brown9-2 · on Nov 12, 2009

Agreed - which makes pointing this out as the first problem in a "gee Google can't write JavaScript article" seems a bit overblown.

manvsmachine · on Nov 12, 2009

In a case like this, it doesn't really matter how much of a performance benefit you get because it's ridiculously trivial to inmplement. This in particular is one of those optimizations that I remember being told back in CS101.