TypeError: undefined is not a function in Angular Resource

Question

When trying to poll a custom method copies on an AngularJS Resource I get the following error at angular.js:10033: (The method copy works just fine.)

TypeError: undefined is not a function
at https://code.angularjs.org/1.3.0-beta.8/angular-resource.min.js:9:347
at Array.forEach (native)
at q (https://code.angularjs.org/1.3.0-beta.8/angular.min.js:7:280)
at q.then.p.$resolved (https://code.angularjs.org/1.3.0-beta.8/angular-resource.min.js:9:329)
at J (https://code.angularjs.org/1.3.0-beta.8/angular.min.js:101:5)
at J (https://code.angularjs.org/1.3.0-beta.8/angular.min.js:101:5)
at https://code.angularjs.org/1.3.0-beta.8/angular.min.js:102:173
at g.$eval (https://code.angularjs.org/1.3.0-beta.8/angular.min.js:113:138)
at g.$digest (https://code.angularjs.org/1.3.0-beta.8/angular.min.js:110:215)
at g.$apply (https://code.angularjs.org/1.3.0-beta.8/angular.min.js:113:468)

Angular.js 10016 - 10035:

function consoleLog(type) {
  var console = $window.console || {},
      logFn = console[type] || console.log || noop,
      hasApply = false;

  // Note: reading logFn.apply throws an error in IE11 in IE8 document mode.
  // The reason behind this is that console.log has type "object" in IE8...
  try {
    hasApply = !!logFn.apply;
  } catch (e) {}

  if (hasApply) {
    return function() {
      var args = [];
      forEach(arguments, function(arg) {
        args.push(formatError(arg));
      });
      return logFn.apply(console, args); // This is line 10033 where the error gets thrown.
    };
  }

Simplified resource:

angular.module('vgm.content-pages')
.factory('ContentPage', function($resource, $http) {

  return $resource('/api/content-page/:id', { id:'@page.id' }, {
    copy: {
      method: 'POST',
      url: '/api/content-page/copy/:id'
    },
    copies: {
      method: 'GET',
      isArray: true,
      url: '/api/content-page/copies/:id'
    }
  });

});

Simplified directive where I'm getting the error:

angular.module('vgm.genericForms')
.directive('vgmFormCopyPicker', function() {

  return {
    restrict: 'E',
    replace: true,
    templateUrl: '/static/common/generic-forms/widgets/view-copy-picker.html',
    scope: {
      resource: '=',
    },
    controller: function($scope, $element) {

      $scope.pages = [];

      $scope.loadCopies = function() {

        $scope.resource.$copies()
          .then(function(response) {
            $scope.pages = response.data;
          });

      };

    }
  };

});

As soon as I run the loadCopies method, executing the line $scope.resource.$copies() throws the error above.

In the Chrome Inspector I see the call to my API is actually being done. But resolving the promise seems to throw some error...

How can I solve this error?

EDIT:

$scope.resource = ContentPage.get({id: $stateParams.id}).$promise
$scope.resource.$save() // Works
$scope.resource.$update() // Works
$scope.resource.$copy() // Works
$scope.resource.$copies() // Does not work!

Angular Resource is trying to overwrite my initial resource with an array of items. But the instance of Resource does not have a method push of course.

Answer 1

I found the answer:

A resource is supposed to represent the matched data object for the rest of its lifespan. If you want to fetch new data you should do so with a new object.

$scope.copies = ContentPage.copies()