Edit in JSFiddle

//add a custom event to the Backbone object
Backbone.on('sayHi', function () {

//create an eavesdropper object and extend the object with Backbone.Events
var eavesdropper = _.extend({}, Backbone.Events);

//Set eavesdropper to listen for custom sayHi event attached to Backbone object
eavesdropper.listenTo(Backbone, 'sayHi', function () {
    console.log('I heard that');

//Trigger/Invoke the sayHi custom event
Backbone.trigger('sayHi'); //logs 'Hi' and 'I heard that'

/*Remember Backbone extended the Backbone namespace with events 
(i.e. cause Backbone did this: _.extend(Backbone, Backbone.Events);)*/