How can do Form Validation in JavaScript

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<HTML>
<HEAD>
<TITLE> Validation Form </TITLE>
<script language="JavaScript" type="text/javascript">
function validate(){
var frmvalidator = new Validator("myform");
frmvalidator.addValidation("FirstName","req","Please enter your First Name");
frmvalidator.addValidation("FirstName","maxlen=20","Max length for FirstName is 20");
frmvalidator.addValidation("FirstName","alpha");

frmvalidator.addValidation("LastName","req");
frmvalidator.addValidation("LastName","maxlen=20");

frmvalidator.addValidation("Email","maxlen=50");
frmvalidator.addValidation("Email","req");
frmvalidator.addValidation("Email","email");

frmvalidator.addValidation("Phone","maxlen=50");
frmvalidator.addValidation("Phone","numeric");

frmvalidator.addValidation("Address","maxlen=50");
frmvalidator.addValidation("Country","dontselect=0");
}
</script>
<META NAME="Generator" CONTENT="EditPlus">
<META NAME="Author" CONTENT="">
<META NAME="Keywords" CONTENT="">
<META NAME="Description" CONTENT="">
</HEAD>

<BODY>
<form action="" name="myform" action="val.htm" onSubmit="validate()">
<table cellspacing="2" cellpadding="2" border="0">
<tr>
<td align="right">First Name</td>
<td><input type="text" name="FirstName"></td>
</tr>
<tr>
<td align="right">Last Name</td>
<td><input type="text" name="LastName"></td>
</tr>
<tr>
<td align="right">EMail</td>
<td><input type="text" name="Email"></td>
</tr>
<tr>
<td align="right">Phone</td>
<td><input type="text" name="Phone"></td>
</tr>
<tr>
<td align="right">Address</td>
<td><textarea cols="20" rows="5" name="Address"></textarea></td>
</tr>
<tr>
<td align="right">Country</td>
<td>
<SELECT name="Country">
<option value="" selected>[choose yours]
<option value="008">Albania
<option value="012">Algeria
<option value="016">American Samoa
<option value="020">Andorra
<option value="024">Angola
<option value="660">Anguilla
<option value="010">Antarctica
<option value="028">Antigua And Barbuda
<option value="032">Argentina
<option value="051">Armenia
<option value="533">Aruba
</SELECT>
</td>
</tr>
<tr>
<td align="right"></td>
<td><input type="submit" value="Submit" ></td>
</tr>
</table>
</form>

</BODY>
</HTML>

If i enter nothing to the form element like text, the javascript validator can't know this, and the form can be submit without entered anything.
why?
how can i do to avoid this?

I am guessing your problem is here:

onsubmit="validate()"

You do not have a return statement here. You need to add the return.

onsubmit="return validate()"

Eric