Backbone loading spinner

Loading spinner implementation in backbone

var BaseView = Backbone.View.extend({
   initialize: function(options) {
      this.init_loader();
   }

   init_loader: function() {
      this.loader = {};
      Backbone.View.prototype.on('workstart', this.start_work, this);
      Backbone.View.prototype.on('workcomplete', this.end_work, this);
      this.loader = new LoaderView();
      $('body').append(this.loader.render().el);
      this.loader.tasks = 0;
      this.loader.modalTasks = 0;
   },

   start_work: function(opt){
      console.log(opt)
      opt = opt || {};
      if (opt.count == null) opt.count = 1;
      if (opt.isModal == null) opt.isModal = false;
      var originalTasks = this.loader.tasks;
      var originalModalTasks = this.loader.modalTasks;
      if (opt.isModal)
      {
         this.loader.modalTasks += opt.count;
         if (originalModalTasks == 0 && this.loader.modalTasks > 0)
         {
            console.log('Displaying modal loader.')
            this.loader.showModal();
         }
      }
      else
      {
         this.loader.tasks += opt.count;
         if (originalTasks == 0 && this.loader.tasks > 0)
         {
            console.log('Displaying spinner loader.')
            this.loader.showSpinner();
         }
      }
      console.log('Started ' + opt.count + ' work items. In queue: ' + (this.loader.tasks + this.loader.modalTasks));
   }, 

   end_work: function(opt)
   {
      opt = opt || {};
      if (opt.count == null) opt.count = 1;
      if (opt.isModal == null) opt.isModal = false;
      var originalTasks = this.loader.tasks;
      var originalModalTasks = this.loader.modalTasks;
      if (opt.isModal)
      {
         this.loader.modalTasks -= opt.count;
         if (originalModalTasks > 0 && this.loader.modalTasks == 0)
         {
            console.log('Hiding modal loader.')
            this.loader.hideModal();
         }
      }
      else
      {
         this.loader.tasks -= opt.count;
         if (originalTasks > 0 && this.loader.tasks == 0)
         {
            console.log('Hiding spinner loader.')
            this.loader.hideSpinner();
         }
      }
      if (this.tasks < 0 || this.modalTasks < 0) 
      {
         throw "Loader has a negative number of work items in its queue. This should never happen."
      }
      console.log('Ended ' + opt.count + ' work items. In queue: ' + (this.loader.tasks + this.loader.modalTasks));
   }
 }
var LoaderView = Backbone.View.extend({
   template: "#base_loader_template",
   tagName: "div",
   id: "loader",
   className: "hide",

   showModal: function()
   {
      throw "Not implemented."
   },

   hideModal: function()
   {
      throw "Not implemented."
   },

   showSpinner: function()
   {
      this.$el.show();
   },

   hideSpinner: function()
   {
      this.$el.hide();
   }

});

// Now to call it in code:

var selected_campaigns = this.get_selected_campaigns();
 this.trigger('workstart', {count: selected_campaigns.length});
 this.collection.move_campaigns_to_group(selected_campaigns, campaign_group_id, campaign_group_name, function() {
    that.trigger('workcomplete');
 });