Array.prototype.myReduce = function () {
let newArr = ;
for (let item of this) {
   if (Array.isArray(item)) {
       newArr = newArr.concat(item.myReduce());
        } else {
            newArr.push(item);
            }
    }
return newArr;
};
// 多维数组
let arr = ]]]];
 console.log(arr.myReduce());