main_controller.js

$(function($) {
  var MainController = App.Controllers.MainController = {
    index: function() {
      console.log("in MainController#index");
    },
    show: function(id) {
      console.log("in MainController#show", id);
    }
  }
});

router.js

$(function($) {
    'use strict';

    var MainRouter = App.Routers.MainRouter = Backbone.Router.extend({
        routes: {
            '': App.Controllers.MainController.index,
            'show/:id': App.Controllers.MainController.show
        }
    });
});