Loop Performance - Cache Array Length, Reference : http://taitems.github.io/Front-End-Development-Guidelines/

LoopPerformance.js

var toLoop = new Array(1000);
 
for (var i = 0; i < toLoop.length; i++) {
    // BAD - the length has to be evaluated 1000 times
}
 
for (var i = 0, len = toLoop.length; i < len; i++) {
    // GOOD - the length is only looked up once and then cached
}