数组的随机排序

function shuffle(arr){

var len = arr.length;

for(var i = 0; i < len - 1; i++){

var idx = Math.floor(Math.random() * (len - i));

var temp = arr[idx];

arr[idx] = arr[len - i - 1];

arr[len - i -1] = temp;

}

return arr;

}