JavaScript统计网页超链接数量的方法

<!DOCTYPE html>
<html>
<body>
<img src ="planets.gif" width="145" height="126" 
alt="Planets" usemap ="#planetmap">
<map name="planetmap">
<area shape="rect" coords="0,0,78,125" href="sun.htm" alt="Sun">
<area shape="circle" coords="88,60,5" href="mercury.htm" alt="Mercury">
<area shape="circle" coords="125,60,9" href="venus.htm" alt="Venus">
</map>
<p><a href="/js/">JavaScript Tutorial</a></p>
<p>Number of areas/links:
<script>
document.write(document.links.length);
</script></p>
</body>
</html>

Number of areas/links: 4