Are loops really faster in reverse?

It’s not that i-- is faster than i++. Actually, they’re both equally fast.

What takes time in ascending loops is evaluating, for each i, the size of your array. In this loop:

for(var i = array.length; i--;)

You evaluate .length only once, when you declare i, whereas for this loop

for(var i = 1; i <= array.length; i++)

you evaluate .length each time you increment i, when you check if i <= array.length.

In most cases you shouldn’t even worry about this kind of optimization.