多判断点试试，JavaScript就是好玩!
<!DOCTYPE HTML>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>prompt</title>
<script language="javascript">
function rec(){
var score; //score变量，用来存储用户输入的成绩值。
score = prompt("请输入你的成绩！",score);
if(score>=90)
{
document.write("你很棒!");
}
else if(score>=75)
{
document.write("不错吆!");
}
else if(score>=60)
{
document.write("要加油!");
}
else if(score == null)
{
document.write("你怎么取消了呢？");
}
else if(score == '')
{
document.write("亲，忘记输入成绩吧!");
}
else if(score<=60)
{
document.write("要努力了!");
}
else
{
document.write("输入不对哦!");
}
}
</script>
</head>
<body>
<form>
<input name="button" type="button" onClick="rec()" value="点击我，对成绩做评价!">
</form>
</body>
</html>
