Sample XHR usage with promises

var do_update, game_state;

game_state = {
  player_id: null,
  last_update_ms: 0,
  score: 0
};

do_update = function() {
  var defer;
  defer = $.Deferred();
  $.ajax({
    url: '/update.php',
    method: 'POST',
    dataType: 'JSON',
    data: {
      last_update: game_state.last_update_ms,
      score: game_state.score
    }
  }).success(function(response) {
    if (!(response && response.success)) {
      defer.reject(response.message || 'Unknown error occured');
      return;
    }
    defer.resolve(response.payload);
  }).error(function(response, code) {
    defer.reject("Server returned " + code);
  });
  return defer.promise();
};

disable_ui();

do_update().always(function() {
  enable_ui();
}).done(function(payload) {
  update_game(payload);
}).fail(function(error) {
  alert("An error occured\n" + error);
});