数组随机打乱

var arr=[1,2,3,4,5,6,7,8];
//    var num=arr.length;
   var arr2=[];
    function random(num){
       return Math.floor(Math.random()*num);
    }
    function ran(arr){
        console.log(arr.length);
        var num=arr.length;
        var a=random(num);
        arr2.push(arr[a]);
        arr.splice(a,1);
        if(num==1){
            console.log(arr2);
        }else{
            ran(arr);
        }
    }
    ran(arr);