Spin.js is a tiny JavaScipt library that helps you create beautiful loading spinners on every web browser up from IE6. It is highly customizable, fast, and has zero dependencies. I'm using it in my AngularJS application to display loading spinners inside my ng-views while my REST API responds with the data the view needs to render itself.

I add a viewLoading boolean to the $scope of each controller that talks to the REST API. The initial value of viewLoading is true.

angular.module('MyApplication')
  .controller('MakesTonsOfAPICallsController', function($scope) {
    $scope.viewLoading = true;
  });

After all the API calls complete successfully, I set viewLoading to false.

angular.module('MyApplication')
  .controller('MakesTonsOfAPICallsController', function($scope, MyLargeModel) {
    $scope.viewLoading = true;

    // Grab all MyLargeModel objects.
    MyLargeModel.get({}, function(result) {
      // Do something with the result.
      $scope.viewLoading = false;
    });
  });

If I have to make multiple calls, I use the $q service to create a promise for each of them. Each promise is resolved or rejected depending on the status code that the API call returns. I then use $q.all() to call a function when all of the promises have been resolved. This function sets viewLoading to false. I will talk more about $q in another post, but here is a rather simplistic example for now:

$q.all([promise1, promise2 ... promiseN]).then(function(data) {
  $scope.viewLoading = false;
});

I want the loading spinner to be displayed for as long as $viewLoading is true, and be replaced by the actual view content as soon as viewLoading becomes false. I use a directive to do this. This is what the markup looks like:

<div ng-controller="MakesTonsOfAPICallsController">
  <div my-loading-spinner="viewLoading">
    <!-- actual view content goes here. -->
  </div>
</div>

And this is what the directive looks like:

angular.module('MyApplication')
  .directive('myLoadingSpinner', function() {
    return {
      restrict: 'A',
      replace: true,
      transclude: true,
      scope: {
        loading: '=myLoadingSpinner'
      },
      templateUrl: 'directives/templates/loading.html',
      link: function(scope, element, attrs) {
        var spinner = new Spinner().spin();
        var loadingContainer = element.find('.my-loading-spinner-container')[0];
        loadingContainer.appendChild(spinner.el);
      }
    };
  });

For this to work correctly, the Spin.js code has to be loaded before the directive code.

The directive is restricted to attributes only and replaces the original content on the page with the content from my template. I set transclude to true so I can re-insert the original content back into the page later. If you look back at the HTML for the view, you will find that the value of the myLoadingSpinner attribute is viewLoading. When Angular encounters our markup, it will create a two-way binding between the loading variable in the directive's scope and the viewLoading variable in the parent controller's scope. If you find this confusing, you may want to read about directives on the AngularJS website.

Before I explain the link function, take a look at the directive's template:

<div>
  <div ng-show="loading" class="my-loading-spinner-container"></div>
  <div ng-hide="loading" ng-transclude></div>
</div>

The markup is simple enough. The div with class my-loading-spinner-container is displayed when loading is true, and hidden if it is false. The second div is hidden if loading is true, and displayed if it is false. The second div also uses ng-transclude to re-include into the page the original content that was replaced by our directive.

Finally, the link function creates a new loading spinner, finds the div with the class my-loading-spinner-container, and puts the spinner inside the div. Hence, the spinner is displayed as long as loading is true, and the actual content is shown when it becomes false, which is exactly what we want.