The Backbone.Marionette.Application object is the hub of your composite application. It organizes, initializes and coordinate the various pieces of your app. It also provides a starting point for you to call into, from your HTML script block or from your JavaScript files directly if you prefer to go that route.

The Application is meant to be instantiated directly, although you can extend it to add your own functionality.

js MyApp = new Backbone.Marionette.Application();

Adding Initializers

Your application needs to do useful things, like displaying content in your regions, starting up your routers, and more. To accomplish these tasks and ensure that your Application is fully configured, you can add initializer callbacks to the application.

```js MyApp.addInitializer(function(options){ // do useful stuff here var myView = new MyView({ model: options.someModel });; });

MyApp.addInitializer(function(options){ new MyAppRouter(); Backbone.history.start(); }); ```

These callbacks will be executed when you start your application, and are bound to the application object as the context for the callback. In other words, this is the MyApp object, inside of the initializer function.

The options parameters is passed from the start method (see below).

Initializer callbacks are guaranteed to run, no matter when you add them to the app object. If you add them before the app is started, they will run when the start method is called. If you add them after the app is started, they will run immediately.

Application Event

The Application object raises a few events during its lifecycle, using the Marionette.triggerMethod function. These events can be used to do additional processing of your application. For example, you may want to pre-process some data just before initialization happens. Or you may want to wait until your entire application is initialized to start the Backbone.history.

The events that are currently triggered, are:

  • **”initialize:before” / onInitializeBefore **: fired just before the initializers kick off
  • **”initialize:after” / onInitializeAfter **: fires just after the initializers have finished
  • “start” / ``onStart``: fires after all initializers and after the initializer events

```js MyApp.on(“initialize:before”, function(options){ options.moreData = “Yo dawg, I heard you like options so I put some options in your options!” });

MyApp.on(“initialize:after”, function(options){ if (Backbone.history){ Backbone.history.start(); } }); ```

The options parameter is passed through the start method of the application object (see below).

Starting An Application

Once you have your application configured, you can kick everything off by calling: MyApp.start(options).

This function takes a single optional parameter. This parameter will be passed to each of your initializer functions, as well as the initialize events. This allows you to provide extra configuration for various parts of your app, at initialization/start of the app, instead of just at definition.

```js var options = { something: “some value”, another: “#some-selector” };

MyApp.start(options); ```

app.vent: Event Aggregator

Every application instance comes with an instance of Marionette.EventAggregator called app.vent.

```js MyApp = new Backbone.Marionette.Application();

MyApp.vent.on(“foo”, function(){ alert(“bar”); });

MyApp.vent.trigger(“foo”); // => alert box “bar” ```

See the `Marionette.EventAggregator <./>`_ documentation for more details.

Regions And The Application Object

Marionette’s Region objects can be directly added to an application by calling the addRegions method.

There are three syntax forms for adding a region to an application object.

jQuery Selector

The first is to specify a jQuery selector as the value of the region definition. This will create an instance of a Marionette.Region directly, and assign it to the selector:

js MyApp.addRegions({   someRegion: "#some-div",   anotherRegion: "#another-div" });

Custom Region Type

The second is to specify a custom region type, where the region type has already specified a selector:

```js MyCustomRegion = Marionette.Region.extend({ el: “#foo” });

MyApp.addRegions({ someRegion: MyCustomRegion }); ```

Custom Region Type And Selector

The third method is to specify a custom region type, and a jQuery selector for this region instance, using an object literal:

```js MyCustomRegion = Marionette.Region.extend({});


someRegion: { selector: “#foo”, regionType: MyCustomRegion },

anotherRegion: { selector: “#bar”, regionType: MyCustomRegion }

}); ```

Removing Regions

Regions can also be removed with the removeRegion method, passing in the name of the region to remove as a string value:

js MyApp.removeRegion('someRegion');

Removing a region will properly close it before removing it from the application object.

For more information on regions, see the region documentation