title: BackboneJS - How to add a Progressbar while fetching collection
body: <p>I have an Backbone App where I fetch different collections by clicking a Letter from a list. So, I want to add a Progressbar or some kind of rotating image but I dont know how to do this.</p>
  
  <p>My View looks like this</p>
  
  <pre><code>function (App, Backbone) {
  
      var Artists = App.module();
      var ArtistView = Backbone.View.extend({
          tagName : 'li',
          template: 'artistItem',
          serialize: function() {
              var data = this.model.toJSON();
              data.letter = this.model.collection.letter;
  
              return data;
          },  
      });
  
      Artists.View = Backbone.View.extend({
          tagName  : 'ul',
          className : 'artistList',
          initialize: function() {
              this.listenTo(this.collection, 'all', this.render);
              this.listenTo(App, 'navigateLetter', this.updateState);
          },
          beforeRender: function() {
              var self = this;
  
              this.collection.each(function(item) {
                  self.insertView(new ArtistView({model: item}))
              })
          },
          updateState: function(letter) {
              this.collection.letter = letter;
              this.stopListening(this.collection);
              this.collection.fetch();
              this.listenTo(this.collection, 'all', this.render);
          }   
      });
      Artists.ArtistsCollection = Backbone.Collection.extend({
          url: function() {
              return '/projects/mdk/index.php/api/artists/' + this.letter; 
          }
      });
  
      return Artists;
  });
  </code></pre>
  
  <p>So does anyone have an idea how to do this? I could imagine I should do something in initialize or beforeRender?</p>
  
  <p>Thanks in advance</p>