返回文档的第一个链接

<img src="/examples/planets.gif" width="145" height="126" alt="Planets" usemap="#planetmap">

<map name="planetmap">

<area id="sun" shape="rect" coords="0,0,82,126" href="/examples/sun.htm" alt="Sun">

<area id="mercury" shape="circle" coords="90,58,3" href="/examples/mercur.htm" alt="Mercury">

<area id="venus" shape="circle" coords="124,58,8" href="venus.htm" alt="Venus">

</map>

<p><a id="javascript" href="/js/">JavaScript 教程</a></p>

<p>第一个链接/地址的ID：

  <script>

    document.write(document.links[0].id);

  </script>

</p>