Handling $http AngularJS return data

Here is client side in AngularJS (works fine):

$scope.ajaxLogin = function(){
    var fn = document.getElementById("username").value;
    var pw = document.getElementById("password").value;
    $http({
        url: "myurl", 
        method: "POST",
        headers: {'Content-Type': 'application/x-www-form-urlencoded'},
        data: { username: fn, password: pw }
    }).success(function(data, status, headers, config) {
        // this callback will be called asynchronously
        // when the response is available
        $scope.showAlertError();
    }).error(function(data, status, headers, config) {
        // called asynchronously if an error occurs
        // or server returns response with an error status.
        $scope.showAlertError();
    });
};

I expect to have success only if user and password are matched. Server side:

if ($result=mysqli_query($con,$sql))
{     
    $rowcount=mysqli_num_rows($result);
    printf($rowcount);
    mysqli_free_result($result);
}

Before AngularJS I used normal AJAX handling. this is how i did earlier:

  function ajax_post(){
      // Create our XMLHttpRequest object
      var hr = new XMLHttpRequest();
      // Create some variables we need to send to our PHP file
      var url = "myurl";
      var fn = document.getElementById("username").value;
      var ln = document.getElementById("password").value;
      var vars = "username="+fn+"&password="+ln;
      hr.open("POST", url, true);
      // Set content type header information for sending url encoded variables in the request
      hr.setRequestHeader("Content-type", "application/x-www-form-urlencoded");
      // Access the onreadystatechange event for the XMLHttpRequest object
      hr.onreadystatechange = function() {
        if(hr.readyState == 4 && hr.status == 200) {
          var return_data = hr.responseText;

        if(return_data=="1"){

          console.log("this is return data"+return_data);

        }else{

          ons.notification.alert({message: 'Login Failed!'});

        }

        }
      }
      // Send the data to PHP now... and wait for response to update the status div
      hr.send(vars); // Actually execute the request

  }

How can I use this with AngularJS? I tried putting similar code in success handler, but it always goes to else block.