var a = [1,2,3,4,5,6,7,8,9,10];

console.time('testing_forward');
for (var i = 0; i < a.length; i++);
console.timeEnd('testing_forward');
// output: testing_forward: 0.041ms

console.time('testing_backwards');
for (var i = a.length - 1; i >= 0; i--);
console.timeEnd('testing_backwards');
// output: testing_backwards: 0.030ms