TemplateHelper in CompositeView

single_view.js

Single.ProductItemView = Marionette.CompositeView.extend({
  templateHelpers: function () {
    return {
        image: function () {
          var image = this.model.getPreviewImage();
          if (image) {
            return image.get('large_url');
          }
          return "";
        }
      }
    }
});