随机打乱数组 Fisher–Yates shuffle

  // Fisher–Yates shuffle
    Array.prototype.shuffle = function() {
            var array = this;
            var m = array.length,
                t, i;
            while (m) {
                i = Math.floor(Math.random() * m--);
                t = array[m];
                array[m] = array[i];
                array[i] = t;
            }
            return array;
        }