表单检验的问题

<script language=javascript >

function check_form(oFrm,num)
{
if(oFrm.F0302.value.Trim()=="")
if(num==1 || num==3)
{alert("\"选项名称\"不能为空或全为空格!");
oFrm.F0302.select();
return false;}
else
{alert("\"特征名称\"不能为空或全为空格!");
oFrm.F0302.select();
return false;}

return true;
}
function window.onload()
{
form1.F0302.select();
}
</script>
</head>
<BODY leftmargin="5" topmargin="20" marginwidth="0" marginheight="0">
<center><table width="100%" height="75%" border="0" cellpadding="2" cellspacing="0" ID="Table1">
<form name=form1 action=<%=request.servairables("script_name")%> method=post onSubmit="return check_form(this,'<%=num%>')" ID="Form1">
<tr><td align=right height=25 >字段1</td>
<td><input type=text name=F0301 maxlength=20 value="<%=F0301%>" ID="Text1"><font color=red>&nbsp;*</font></td></tr>
<tr><td align=right height=25>字段2</td><td><input type=text name=F0302 value="<%=F0302%>" ></td></tr>
<input type=submit value="ok">
</form>
</table>
</center>
</BODY></html>