Why is iterating through an array backwards faster than forwards

Question

Given this code:

var arr = [];

for (var i = 0; i < 10000; ++i)
    arr.push(1);

Forwards

for (var i =          


        

Answer 1

i > 0 is faster than i < arr.length and is occurring on each iteration of the loop.

You can mitigate the difference with this:

for (var i = 0, len = arr.length; i < len; ++i) {;
}

This is still not as fast as the backwards item, but faster than your forward option.