loop_array_length.js

// run it using
// node loop_array_length.js
// =>
//    bad 7 ms
//    good 5 ms
var a = []
for (var i = 0; i < 10000000; i++) {
  a.push(i);
}

var bm = function(fn, name) {
  var start = new Date;
  fn()
  console.log(name, (new Date) - start, "ms");
}

bm(function() {
  var len = a.length
  for (var i = 0; i < len; i++) {
    i + 1; //doing some dummy work
  }
}, "good")

bm(function() {
  for (var i = 0; i < a.length; i++) {
    i + 1; //doing some dummy work
  }
}, "bad")