<script language="javascript">
function ykd_kontrol()
{
isim = document.form.isim.value;
soyad = document.form.soyad.value;
 if (isim == "" || soyad == "")
 {
  alert("Lütfen Boş Alan Bırakmayın.");
 }
 else
 {
  document.form.submit;
 }
}
</script>

<form method="post" action="" name="form" id="form">
<input type="text" name="isim" id="isim"><br>
<input type="text" name="soyad" id="soyad"><br>
<input type="button" value="Formu Postala" onClick="ykd_kontrol()">
</form>