<html><body><img id="planets"src="/i/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>