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 itera

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.