泉州结石病医院:判断是否为空

<script language="vbscript">
function checkform()
dim msg
if len(trim(theForm.title.value))=0 then
msg=MsgBox("error",48,"err")
msg.show()
theForm.title.focus()
checkform=false
Exit Function
end if
theForm.submit
end function
</script>
<form id="theForm" name="theForm" method="post" action="message_main.asp" >
<input type="submit" name="Submit" value="提交" onclick=checkForm()>
<input type="reset" name="Submit2" value="重置" /></td>
</form>

虽然是有个对话框弹出，但是它还是会提交，我想要的是弹出对话框确定后，不提交！应该怎么弄！
是不是在BUTTON 里的ONCLICK？？

<script language="vbscript">
function checkform()
dim msg
if len(trim(theForm.title.value))=0 then
msg=MsgBox("error",48,"err")
msg.show()
theForm.title.focus()
Exit Function
else
theForm.submit
end if
end function
</script>
<form id="theForm" name="theForm" method="post" action="message_main.asp" >
<input type="submit" name="Submit" value="提交" onclick=checkForm()>
</form>
这样，它还是提交了，究竟怎么了！！高手请指教下！谢谢！