[-VladK-]

אתה מתכוון ככה:

<script language="JavaScript">
function formCheck(){
if (document.formcheck.FirstName.value.length==0) {
     alert("No FirstName");
     return false;
}
if (document.formcheck.LastName.value.length==0) {
     alert("No LastName!");
     return false;
}
}
</script>
<form name="formcheck" onsubmit="formCheck();">
First Name: <input type=text name="FirstName" size="25"><br>
Last Name: <input type=text name="LastName" size="25"><br>
<input type=submit value="Submit Form">
</form>