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

var midNum = arr.splice(midIndex,1)[0];

var left = [];

var right = [];

for (var i = 0,len = arr.length; i < len; i++) {

if (arr[i] < midNum) {

left.push(arr[i]);

} else {

right.push(arr[i]);

}

}

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

}