How to use the backbone.$ function in backbone

//
// RootView
//

import * as bb from 'backbone';
import * as Radio from 'radio';
import LayoutView from 'base/layout-view';
import FooterView from '../footer-view';
import AuthMenuView from '../menu-views/auth-menu-view';
import UnauthMenuView from '../menu-views/unauth-menu-view';

var authChannel = Radio.channel('auth');

var RootView = LayoutView.extend({
  el: bb.$('body'),

  regions: {
    header: '.menu',
    container: 'main > div',
    footer: 'footer'
  },

  initialize() {
    this.getRegion('footer').show(new FooterView());
    this.showMenu();
    this.listenTo(authChannel, 'logout', this.showMenu);
    var containerRegion = this.getRegion('container');
    Radio.comply('rootView', 'showIn:container', containerRegion.show, containerRegion);
  },

  showMenu() {

this.set((this.defaults || {}));
    this.set((data || {}));

    // Get any additional routes passed in from options
    this.routes =  _.defaults((options.routes || {}), this.routes);

    // Ensure that all route functions exist
    _.each(this.routes, function(value, key, routes){
        if(typeof value !== 'string'){ throw('Function name passed to routes in  ' + this.tagName + ' component must be a string!'); }
        if(!this[value]){ throw('Callback function '+value+' does not exist on the  ' + this.tagName + ' component!'); }
    }, this);


    // Set or create our element and template if we have them
    this.el = el || document.createDocumentFragment();
    this.$el = (_.isFunction(Backbone.$)) ? Backbone.$(this.el) : false;

    // Render our dom and place the dom in our custom element
    this.render();

    // Add active class to this newly rendered template's link elements that require it
    $(this.el).markLinks();

    // Call user provided initialize
    this.initialize();

    return this;
  },

var _          = require('underscore');
var Backbone   = require('backbone');
var middleware = require('../../state/middleware');
var CodeMirror = require('codemirror');

require('./ui');
require('./ajax');
require('./sandbox');
require('./completion');
require('./result-cell');
require('./persistence');
require('./application');
require('./authentication');

// Trigger middleware for keydown events.
Backbone.$(document).on('keydown', function (e) {
  var keyName = CodeMirror.keyName(e, e.which === 16);

  middleware.trigger('keydown:' + keyName, {
    preventDefault: _.bind(e.preventDefault, e)
  });
});

beforeEach(function() {
    this.setFixtures('<div id="testRegion"></div>');
    this.el = Backbone.$('#testRegion');
    this.myRegion = new Region({
      el: this.el
    });
  });

updateHighlighter(el, pos) {
    var $el = $(el);
    var model = $el.data('model');

    if (
      !model ||
      !model.get('hoverable') ||
      model.get('status') == 'selected'
    ) {
      return;
    }

    var hlEl = this.canvas.getHighlighter();
    var hlStyle = hlEl.style;
    var unit = 'px';
    hlStyle.left = pos.left + unit;
    hlStyle.top = pos.top + unit;
    hlStyle.height = pos.height + unit;

run(editor, sender) {
    this.sender = sender;

    var config = editor.Config;
    var pfx = config.stylePrefix;
    var tm = editor.TraitManager;
    var panelC;

    if (!this.$cn) {
      var tmView = tm.getTraitsViewer();
      var confTm = tm.getConfig();
      this.$cn = $('<div></div>');
      this.$cn2 = $('<div></div>');
      this.$cn.append(this.$cn2);
      this.$header = $('<div>').append(
        `<div class="${confTm.stylePrefix}header">${confTm.textNoElement}</div>`
      );
      this.$cn.append(this.$header);
      this.$cn2.append(
        `<div class="${pfx}traits-label">${confTm.labelContainer}</div>`
      );
      this.$cn2.append(tmView.render().el);
      var panels = editor.Panels;

      if (!panels.getPanel('views-container'))
        panelC = panels.addPanel({ id: 'views-container' });
      else panelC = panels.getPanel('views-container');

      panelC</div>

default: function() {
    this._hideAbout();
    this._hideContribute();
    this._hideAirports();
    this._resetOffset();

    Backbone.$('body').removeClass('detail-open');
  },

componentDidMount: function () {
      Backbone.$(this.getDOMNode()).find("input").focus();
    },

initialize: function(options) {
    this.airports = options.airports;
    this.render();

    this.airports.on('change:visible', this._handleChange, this);

    var self = this;
    Backbone.$(window).scroll(function() {
      self._updateViews(arguments);
    });

    Backbone.$(window).resize(function() {
      self._updateViews(arguments);
    });
  },