算法-洗牌算法（打乱数组）

        let shuffleFn = (arr) =>{
            let index = 0 , n = arr.length;
            while(index < n){
                let rand = index + Math.floor(Math.random() * (n - index));
                [arr[rand] , arr[index]] = [arr[index] , arr[rand]];
                index++;
            }
            return arr;
        }
        console.log(shuffleFn([1,2,3,4,5]))