php overriding my javascript code

I have Form where a user inputs the data, presses submit and the data is saved in MySQL(php). The Form can only be submitted if all the fields are not empty(javascript).

The problem is this: if I use the code without the php(to store the data in mysql), the javascript for checking empty inputs works. If I add my php code, the javascript wont work. I can submit forms even if they are all empty and I don't want that.

The form:

<form action="index.php"  method="post" role="form" onsubmit="return validateForm()">
        <div class="form-group">
    <label for="name">Vardas</label>
    <input type="text" class="form-control" name="name" placeholder="Vardas"  >
  </div>
  <div class="form-group">
    <label for="lastName">Pavardė</label>
    <input type="text" class="form-control" name="lastName"  placeholder="Pavardė" >
  </div>
  <div class="form-group">
    <label for="ak">Asmens kodas</label>
    <input type="text" class="form-control" name="ak"  placeholder="Asmens kodas" >
  </div>
  <div class="form-group">
    <label for="adress">Adresas</label>
    <input type="text" class="form-control" name="adress"  placeholder="Adresas"  >
  </div>
  <div class="form-group">
    <label for="number">Telefono nr.</label>
    <input type="text" class="form-control" name="number"  placeholder="Telefono nr." >
  </div>
   <div class="form-group">
    <label for="email">El. pašto adresas</label>
    <input type="email" class="form-control" name="email"  placeholder="El. paštas" >
  </div>
   <div class="form-group">
    <label for="preke">Prekės pasirinkimas</label>
    <select class="form-control" name="preke" >
        <?php 
        while($preke = mysqli_fetch_array($r)){   //Creates a loop to loop through results
        echo "<option>" . $preke['Pavadinimas'] . "</option>";  //$row['index'] the index here is a field name
}?>

The JavaScript:

<script>
function validateForm() {
    var a = document.forms["myForm"]["name"].value;
    if (a == null || a == "") {
        alert("Visi laukai turi būti užpildyti");
        return false;
    }
 var b = document.forms["myForm"]["lastName"].value;
    if (b == null || b == "") {
        alert("Visi laukai turi būti užpildyti");
        return false;
    }
     var c = document.forms["myForm"]["ak"].value;
    if (c == null || c == "") {
        alert("Visi laukai turi būti užpildyti");
        return false;
    }
     var d = document.forms["myForm"]["adress"].value;
    if (d == null || d == "") {
        alert("Visi laukai turi būti užpildyti");
        return false;
    }
     var e = document.forms["myForm"]["number"].value;
    if (e == null || e == "") {
        alert("Visi laukai turi būti užpildyti");
        return false;
    }
     var f = document.forms["myForm"]["email"].value;
    if (f == null || f == "") {
        alert("Visi laukai turi būti užpildyti");
        return false;
    }
     var g = document.forms["myForm"]["preke"].value;
    if (g == null || g == "") {
        alert("Visi laukai turi būti užpildyti");
        return false;
    }
}
</script>

The PHP:

if(isset($_POST['Submitted']) == 1) {

            $query = "INSERT INTO uzsakymai (Vardas, Pavarde, Ak, Adresas, Telefonas, pastas, preke) VALUES ('$_POST[name]', '$_POST[lastName]','$_POST[ak]','$_POST[adress]','$_POST[number]','$_POST[email]','$_POST[preke]')";
            $result = mysqli_query($dbc, $query);

            if($result) {

                echo '<p>Forma issaugota</p>';

            } else {

                echo '<p>Page could not be added because: '.mysqli_error($dbc);
                echo '<p>'.$query.'</p>';
            }

        }


        ?>