用快捷键来提交按钮，这样比较简单
<html>
<head>
<script language="JavaScript">
//用JS计算您的文胸尺码 网页教学网http://www.knowsky.com
function jisuan()
{
if (document.form1.up.value=='') {
alert ('请填入上胸围的尺寸：');
return false;
}
if (document.form1.up.value=='') {
alert ('请填入下胸围的尺寸：');
return false;
}
var answer=document.form1.up.value-document.form1.under.value;
yushu=document.form1.under.value%10;
if (yushu < 5)
yushu = 0;
if (yushu >= 5)
yushu = 5;
chima='您的文胸尺码为：'+(Math.floor(document.form1.under.value/10)*10+yushu/1);
if (answer <= 10)
chima=chima+'A';
else if (answer <=14 && answer >=11)
chima=chima+'B';
else if (answer <=19 && answer >=14)
chima=chima+'C';
else
chima=chima+'D';
alert (chima);
}
</script>
</head>
<body>
<form name="form1" method="post">
请填入上胸围尺寸：
<input name="up" type="text" size="8">
CM <br>请填入下胸围尺寸：
<input name="under" type="text" size="8">
CM <br>
<input type="submit" name="Submit" value="计算" onclick="jisuan();">
<input type="reset" name="Submit2" value="重填">
</form>
</body>
</html>