翻转函数reverse的原理

function reverse(arr){
      var newArr = []
      for(var i = arr.length -1; i >= 0; i--){
        //   newArr刚开始为空，取到的是0索引，接收arr.length -1索引
          newArr[newArr.length] = arr[i]
      }
      return newArr;
    }
    var na = reverse(['1','2','3','4','5','6']);
    console.log(na);