function cek(){
        var username = $("#username").val();
        var password = $("#password").val();

        if (username == "" && password == "") {
            alert("Username and password can't be empty!");
        }else {
            $.ajax({
                url: "processLogin.php",
                type: "POST",
                data:{
                    username: $("#username").val(), password: $("#password").val()
                },
                success:function(e){
                    alert("e");
                }
            });
        }
    }

$username = $_POST['username'];
$password = $_POST['password'];

$sql = "SELECT * FROM user WHERE nama='$username' AND password='$password'";
$query = $db->query($sql)or die(mysqli_error($db));
$result = $query->fetch_assoc();

if ($query->num_rows == 0) {

    // I want this to be show on alert
    echo "Username not found!";

}else{
    if ($password <> $result['password']) {

        // I want this to be show on alert
        echo "Incorrect password!";

    }else{
        $_SESSION['username'] = $result['nama'];
        $_SESSION['tipe'] = $result['tipe'];
        header('location:index.php');
    }
}