洗牌算法

function shuffle(arr){
    var newArr = [];
    while (arr.length){
        var randomIndex = Math.floor(Math.random() * arr.length);
        newArr.push(arr.splice(randomIndex,1)[0]);
    }
    return newArr;
}

参考：https://juejin.im/post/5cef46226fb9a07eaf2b7516