如何在表内将复选框设置为选中状态

<table>
  <tr>
    <td><input type="checkbox" name="checkbox1"></td>
    <td>行1</td>
  </tr>
  <tr>
    <td><input type="checkbox" name="checkbox2"></td>
    <td>行2</td>
  </tr>
  <tr>
    <td><input type="checkbox" name="checkbox3"></td>
    <td>行3</td>
  </tr>
</table>

<table>
  <tr>
    <td><input type="checkbox" name="checkbox1" checked></td>
    <td>行1</td>
  </tr>
  <tr>
    <td><input type="checkbox" name="checkbox2"></td>
    <td>行2</td>
  </tr>
  <tr>
    <td><input type="checkbox" name="checkbox3"></td>
    <td>行3</td>
  </tr>
</table>

<table>
  <tr>
    <td><input type="checkbox" id="checkbox1" name="checkbox1"></td>
    <td>行1</td>
  </tr>
  <tr>
    <td><input type="checkbox" id="checkbox2" name="checkbox2"></td>
    <td>行2</td>
  </tr>
  <tr>
    <td><input type="checkbox" id="checkbox3" name="checkbox3"></td>
    <td>行3</td>
  </tr>
</table>

<script>
  // 获取复选框元素
  var checkbox1 = document.getElementById("checkbox1");
  
  // 设置复选框选中状态
  checkbox1.checked = true;
</script>