使一个表格单元格填充行

<style>
  td {
    vertical-align: middle;
    height: 30px;
  }
</style>

<table>
  <tr>
    <td>内容</td>
  </tr>
  <tr>
    <td>内容</td>
  </tr>
  <tr>
    <td>内容</td>
  </tr>
</table>

<table>
  <tr>
    <td id="fillCell">内容</td>
  </tr>
  <tr>
    <td>内容</td>
  </tr>
  <tr>
    <td>内容</td>
  </tr>
</table>

<script>
  var fillCell = document.getElementById("fillCell");
  var fillHeight = fillCell.offsetHeight;

  var cells = document.getElementsByTagName("td");
  for (var i = 0; i < cells.length; i++) {
    cells[i].style.height = fillHeight + "px";
  }
</script>