validasi username

 <script type="text/javascript">
$("#driverForm").validate({
  rules: {
   akun: {
      required: true,
      minlength: 4
},
  messages: {
   akun: {
      minlength: "<div class='text-danger'>Nama akun minimal 4 karakter</div>"
});
</script> 

<?php  
if(isset($_POST['submit'])){
 $username = $_POST['username'];
 $password = $_POST['password'];
 if(!empty(trim($username)) && !empty(trim($password))){
  if(strlen($username) >= 4 && strlen($password) >= 4 ){
   echo "Berhasil";
  }else{
   echo "Gagal, username dan password anda kurang dari 4 karakter";
  }
 }else{
  echo "Form jangan dikosongkan";
 }
}
?>