onmouseover 事件
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<head>
<meta charset="utf-8">
<title>滴答编程(dida100.com)</title>
<script>
function writeText(txt){
document.getElementById("desc").innerHTML=txt;
}
</script>
</head>
<body>
<img src ="planets.gif" width ="145" height ="126" alt="Planets" usemap="#planetmap" />
<map name="planetmap">
<area shape ="rect" coords ="0,0,82,126"
onmouseover="writeText('太阳和气体巨星类似木星是太阳系中最大的物体。')"
href ="sun.htm" target ="_blank" alt="Sun" />
<area shape ="circle" coords ="90,58,3"
onmouseover="writeText('从地球上很难研究水星，因为它太接近太阳。')"
href ="mercur.htm" target ="_blank" alt="Mercury" />
<area shape ="circle" coords ="124,58,8"
onmouseover="writeText('至到1960年，金星经常被认为是地球的孪生妹妹，因为金星是最靠近我们的行星，并且两个行星有很多相似的特点。')" t')"
href ="venus.htm" target ="_blank" alt="Venus" />
</map>
<p id="desc">鼠标在太阳和星星上移动，可以看到不同的描述。</p>
</body>
</html>