code: function InfiniteScrollSetup (options) {
    options || (options = {});
    var self = this;
    var gap = (options.gap || 20); // defaults to 20
  
    self.events = self.events || {};
    assign(self.events, {scroll: 'infiniteScroll'});
  
    self.infiniteScroll = function () {
      if (this.el.scrollHeight - this.el.scrollTop <= this.el.clientHeight + gap) {
        this.collection.fetchPage(options);
      }
    };
  }
docs: Setup the closure function for the Infinite Scroll callback
  
  @param {Object}  options - the valid options are:
  .gap - the pixel margin to fire the request