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Code
<script language="JavaScript">
function check()
{
if(parseInt(document.form1.num.value )> 10)
{
alert("!")
return false
}
}
</script>
<form id="form1" name="form1" method="post" action="ask.asp" onsubmit="return check();" >
<input type="text" id="num" name="num" value="5" style="height:20px; width:100px" >
<input type="submit" name="btn" id="btn" value="开始测试" />
</form>