如何判断一个tr元素是否在可视范围内。

从 scrollTop 到 clientHeight+scrollTop 当前显示的纵坐标范围

解决方案 »

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谢谢小康。var row =document.getElementById("firstRow");
row.style.position="absolute";
if((row.*** >document.body.scrollTop)&&
(row.***<document.body.clientHeight+document.body.scrollTop))
{ row 可见。
}我想知道这个row.***到底应该是tr的什么属性。谢谢。
row.scrollTop的值始终都是0,没有变化。奇怪。
下面是页面的源程序，请高手帮忙调试一下。谢谢。
<html>
<script type="text/javascript">

</script>
<body >
<br>
<br>
<br>
<br>
<input type ="text" name ="t" id="t"/>
<table border="1" id="tb" cellpadding="2" cellspacing="0">
  <tr id = "firstRow" bgColor="red">
    <th>
      name
    </th>
    <th>
      value
    </th>
    <th>
      meaning
    </th>
  </tr>
  <tr>
    <th>
      <code>
        src
      </code>
    </th>
    <td>
      <code>
        "
      </code>
      <var>
        URL
      </var>
      <code>
        "
      </code>
    </td>
    <td>
      the address of the initial content for the inline frame
    </td>
  </tr>
  <tr>
    <th>
      <code>
        name
      </code>
    </th>
    <td>
      <code>
        "
      </code>
      <var>
        string
      </var>
      <code>
        "
      </code>
    </td>
    <td>
      assigns a name to the inline frame, for
      <a href="#target">        use in
        <code>
          target
        </code>
        attribute</a>
    </td>
  </tr>
  <tr>
    <th>
      <code>
        longdesc
      </code>
    </th>
    <td>
      <code>
        "
      </code>
      <var>
        URL
      </var>
      <code>
        "
      </code>
    </td>
    <td>      refers to a document containing a description (not supported yet)
    </td>
  </tr>
  <tr>
    <th>
      <code>
        width
      </code>
    </th>
    <td rowspan="2">
      number of pixels or percentage (e.g.
      <code>
        "20%"
      </code>      )
    </td>
    <td>
      width of the inline frame; see
      <a href="#dim" title="Dimensions">        notes below</a>
    </td>
  </tr>
  <tr>
    <th>
      <code>
        height
      </code>
    </th>
    <td>
      height of the inline frame; see
      <a href="#dim" title="Dimensions">        notes below</a>
    </td>
  </tr>
  <tr>
    <th rowspan="5">
      <code>
        align
      </code>
    </th>
    <td>
      <code>
        "top"
      </code>
    </td>
    <td>      aligns the inline frame vertically on the top of the surrounding
      content on its left and right
    </td>
  </tr>
  <tr>
    <td>
      <code>
        "bottom"
      </code>
    </td>
    <td>      aligns the inline frame vertically on the bottom of the
      surrounding content on its left and right
    </td>
  </tr>
  <tr>
    <td>
      <code>
        "middle"
      </code>
    </td>
    <td>      aligns the center of the inline frame vertically with the current
      baseline
    </td>
  </tr>
  <tr>
    <td>
      <code>
        "left"
      </code>
    </td>
<td>      places the inline frame at the left margin so that subsequent
      page content flows on the right of it
    </td>
  </tr>
  <tr>
    <td>
      <code>
        "right"
      </code>
    </td>
    <td>      places the inline frame at the right margin so that subsequent
      page content flows on the left of it
    </td>