shuffle.js

function shuffle(arr) {
   if (!Array.isArray(arr)) { throw "need an array as input"; }
   if (arr.length < 2) { return arr; }
   var pick = Math.floor(Math.random() * (arr.length));
   var tmp = arr[pick]; arr[pick] = arr[0]; arr[0] = tmp;
   return [arr[0]].concat(shuffle(arr.slice(1)));
 }
 shuffle([1,2,3,4,5])