The Mediator pattern enables communication (mediation) between views using a mediator object.

The mediator inside is extend  Backbone mediator and come with Oro Platform in the path vendor/oro/platform/src/Oro/Bundle/UIBundle/Resources/public/js/mediator.js , So you can use by calling inside your custom js by :
   

 
      var mediator = require('oroui/js/mediator');
   

So the mediator trigger many events like :

 
   mediator.trigger('cms:content-variant-collection:add', this.$el);
   mediator.trigger('checkout-content:updated');
 

Is clean trigger every new content variations added in Content block , the second trigger any content update in checkout step .

So exist too some other with after and before like:

 
   mediator.trigger('checkout-content:before-update'); 
 

How you can Listen Event with mediator:

first method is using on function:

 
        initialize: function() {
            mediator.on('checkout-content:updated', this._onContentUpdated, this);
        }
 

and add you function :

 
        _onContentUpdated: function() {
           //some code;
        }
 

 
        dispose: function() {
            if (this.disposed) {
                return;
            }
            mediator.off('checkout-content:updated', this._onContentUpdated, this);
        }
 

 
        listen: {
            'grid_load:complete mediator': 'onGridLoadComplete'
        }
 

 
        onGridLoadComplete: function(collection) {
            //some code
        }
 

Full example of Listening add to shopping cart:

 
define(function(require) {
    'use strict';
    var AddShoppingListDetectorComponent;
    var BaseComponent = require('oroui/js/app/components/base/component');
    var mediator = require('oroui/js/mediator');
    var routing = require('routing');
    var _ = require('underscore');
    AddShoppingListDetectorComponent = BaseComponent.extend({
        /**
         * @inheritDoc
         */
        listen: {
            'shopping-list:line-items:update-response mediator': '_onLineItemAdd'
        },
        /**
         * @inheritDoc
         */
        constructor: function AddShoppingListDetectorComponent() {
            AddShoppingListDetectorComponent.__super__.constructor.apply(this, arguments);
        },
        _onLineItemAdd: function(model, response) {
             //Some code
        }
    });
   return AddShoppingListDetectorComponent;
});
 

Is simple code .