javaScipt validation

<script type="text/javascript">
 function submitLeadForm()
 {
  var form = document.getElementById('leadForm');
  var regEmail = /^([A-Za-z0-9_\-\.])+\@([A-Za-z0-9_\-\.])+\.([A-Za-z]{2,4})$/;
        if(form.email.value=='' || !regEmail.test(form.email.value))
  {
   alert('Please fill your email address');
   form.email.focus();
   return false;
  }
  if(form.mobile.value=='' || isNaN(form.mobile.value))
  {
   alert('Please enter valid mobile no.');
   form.mobile.focus();
   return false;
  }

  if(form.mobile.value.length<10)
  {
   alert('Please enter 10 digit mobile no.');
   form.mobile.focus();
   return false;
  }

  return true;
 }
</script>