function quickSort(arr){

if(arr.length <= 1) return arr;

var index = Math.floor(arr.length/2);

var key = arr.splice(index,1)[0];

var left = [],right = [];

arr.forEach(function(v){

   v <= key ? left.push(v) : right.push(v);

});

return quickSort(left).concat([key],quickSort(right));

}