var shuffled = str.split('').sort(function(){return 0.5-Math.random()}).join('');
String.prototype.shuffle = function () {
var a = this.split(""),
n = a.length;
for(var i = n - 1; i > 0; i--) {
var j = Math.floor(Math.random() * (i + 1));
var tmp = a[i];
a[i] = a[j];
a[j] = tmp;
}
return a.join("");
}
console.log("the quick brown fox jumps over the lazy dog".shuffle());
//-> "veolrm hth ke opynug tusbxq ocrad ofeizwj"
console.log("the quick brown fox jumps over the lazy dog".shuffle());
//-> "o dt hutpe u iqrxj yaenbwoolhsvmkcger ozf "