Don't use Array.length in loop conditions

[hampelm]

Per @mr0gorg's comment:

"In most engines, Array.length is calculated dynamically, so you should never use it in the loop's condition during performance-sensitive operations. Something like this is often much faster:

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

This way, the length value is pre-computed and cached in len."