<html>
<body>
<img id="planets"
src="/img/eg_planets.jpg"
usemap="#planetmap" />
<map name="planetmap">
<area id="venus" shape="circle"
coords="180,139,14"
href ="/example/html/venus.html"
target ="_blank"
alt="Venus" />
</map>
<br />
area 元素的 id 是：
<script type="text/javascript">
document.write(document.links[0].id)
</script>
</body>
</html>