Convert $http promise to regular promise

gistfile1.js

    Article.prototype.comments = function() {
      var url = RouteIndex.comments($scope.article.id).relative();
      var deferred = $q.defer();
      $http.get(url).success(function(comments) {
        deferred.resolve(comments);
      });
      return deferred.promise;
    };
    
    //usage
    
    $scope.article.comments().then(function(comments) {
      $scope.comments = comments;
    })