Fisher-Yates Shuffle

shuffle.js

function shuffle(array) {
  var counter = array.length - 1;
  var tmp;
  var index;
  for (; counter > 0; counter--) {
    index = Math.floor(Math.random() * counter);
    tmp = array[counter];
    array[counter] = array[index];
    array[index] = tmp;
  }
}