Using backbone custom events and the observer pattern

backbone.custom.events.js

// app.js, ommitting IIFE's for brevity

APP = {};

_.extend(APP, Backbone.Events);

// views.js

APP.Views.Login = Backbone.View.extend({

  // ... snip
  
  success: function() {
    APP.trigger('login:success'); // anything can listen to this and hook into it
  }

});

// later on, in some other view

APP.Views.Subscription = Backbone.View.extend({

  initialize: function() {
    APP.bind('login:success', this.showSubscriptionDetails);
  },
  
  showSubscriptionDetails: function() {
    // we know login was completed, show the users subscription details
    this.$('.subscription-info').show();
  }

});

except this is pub/sub pattern with topic-based routing ;-)