Question

考虑以下js-loop：

for (var i=0;i<diff;++i){
        for (var j=0; j<old_col_num; ++j){
            var t_col = document.createElement("td");
            //the following line throws an error:
            t_body.children[old_row_num+1+i].appendChild(t_col);    
        }
}

我收到的错误消息如下：

 Uncaught TypeError: Cannot read property 'appendChild' of undefined(…)

我不明白为什么它不起作用。如果我输入一个固定的数字而不是＆＃34; old_row_num + 1 + i＆＃34;没有错误（但我的程序需要灵活性）。

更新：

整个功能如下：

function change_dim_r(diff) {

            var old_row_num = t_body.childElementCount;
            var old_col_num = t_body.children[0].childElementCount;

            for (var i=0; i<diff; ++i){
                var new_t_row = document.createElement("tr");
                t_body.appendChild(new_t_row);
            }

            for (var i=0;i<diff;++i){
                for (var j=0; j<old_col_num; ++j){
                    var t_col = document.createElement("td");
                    t_body.children[old_row_num+1+i].appendChild(t_col);    
                }
            }
 }

Answer 1

我相信您的旧行号不准确。

var old_row_num = t_body.children.childElementCount;

如果您想要行数，那么.children就行了。

＆＃13;

function change_dim_r(diff) {

  var t_body = document.querySelector("tbody");
  var old_row_num = t_body.childElementCount;
  var old_col_num = t_body.children[0].childElementCount;

  for (var i = 0; i < diff; ++i) {
    var new_t_row = document.createElement("tr");
    t_body.appendChild(new_t_row);
  }

  for (var i = 0; i < t_body.childElementCount; ++i) {
    var t_row = t_body.children[i];
    
    for (var j = t_row.childElementCount; j < t_body.childElementCount; ++j) {
      var t_col = document.createElement("td");
      t_row.appendChild(t_col);
    }
  }
}

change_dim_r(10);

＆＃13;

<table border="1" cellpadding="2" cellspacing="2">
  <tbody>
    <tr>
      <td></td>
    </tr>
  </tbody>
</table>

＆＃13;

t_body.children [k] .appendChild（var）抛出错误

1 个答案: