const arr=['i','m','o','o','e']
        //for...of循环数组  entries()方法 索引+值的可遍历对象
        for([index,value] of arr.entries()){
           // console.log(index,value)
           //判断值为'o'时的情况
            if(value==='o'){
                //将值变为大写
              arr[index]=value.toLocaleUpperCase();
              //跳出循环，不然第二个'o'也会变为大写
              break;
            }
        }
        console.log(arr)