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Marionette.Behavior

A Behavior provides a clean separation of concerns to your view logic,
allowing you to share common user-facing operations between your views.

Behaviors are particularly good at factoring out the common user, model and
collection interactions to be utilized across your application.

Documentation Index

Using Behaviors

The easiest way to see how to use the Behavior class is to take an example
view and factor out common behavior to be shared across other views.

var Mn = require('backbone.marionette');

var MyView = Mn.View.extend({
  ui: {
    destroy: '.destroy-btn'
  },

  events: {
    'click @ui.destroy': 'warnBeforeDestroy'
  },

  warnBeforeDestroy: function() {
    alert('You are about to destroy all your data!');
    this.destroy();
  },

  onRender: function() {
    this.ui.destroy.tooltip({
      text: 'What a nice mouse you have.'
    });
  }
});

Live example

Interaction points, such as tooltips and warning messages, are generic concepts.
There is no need to recode them within your Views so they are prime candidates
to be extracted into Behavior classes.

Defining and Attaching Behaviors

var Mn = require('backbone.marionette');

var DestroyWarn = Mn.Behavior.extend({
  // You can set default options
  // just like you can in your Backbone Models.
  // They will be overridden if you pass in an option with the same key.
  defaults: {
    message: 'You are destroying!'
  },
  ui: {
    destroy: '.destroy-btn'
  },

  // Behaviors have events that are bound to the views DOM.
  events: {
    'click @ui.destroy': 'warnBeforeDestroy'
  },

  warnBeforeDestroy: function() {
    var message = this.getOption('message');
    window.alert(message);
    // Every Behavior has a hook into the
    // view that it is attached to.
    this.view.destroy();
  }
});

var ToolTip = Mn.Behavior.extend({
  defaults: {
    text: ''
  },
  ui: {
    tooltip: '.tooltip'
  },

  onRender: function() {
    this.ui.tooltip.tooltip({
      text: this.getOption('text')
    });
  }
});

We've passed in a defaults attribute that sets default options.
This will be covered in default soon. With the warning and tooltip
behaviors extracted, we just need to attach them to our view:

var Mn = require('backbone.marionette');

var MyView = Mn.View.extend({
  behaviors: [DestroyWarn, ToolTip]
});

Live example

Each behavior will now be able to respond to user interactions as though the
event handlers were attached to the view directly. In addition to using array
notation, Behaviors can be attached using an object:

var Mn = require('backbone.marionette');

var MyView = Mn.View.extend({
  behaviors: {
    destroy: DestroyWarn,
    tooltip: ToolTip
  }
});

Behavior Options

When we attach behaviors to views, we can also pass in options to add to the
behavior. This tends to be static information relating to what the behavior
should do. In our above example, we want to override the message to our
DestroyWarn and Tooltip behaviors to match the original message on the View:

var Mn = require('backbone.marionette');

var MyView = Mn.View.extend({
  behaviors: [
    {
      behaviorClass: DestroyWarn,
      message: 'You are about to destroy all your data!'
    },
    {
      behaviorClass: ToolTip,
      text: 'What a nice mouse you have.'
    }
  ]
});

Live example

Using an object, we must define the behaviorClass attribute to refer to our
behaviors and then add any extra options with keys matching the option we want
to override. Any passed options will override the defaults passed.

Here is the syntax for declaring which behaviors get used within a View.

var Mn = require('backbone.marionette');

var MyView = Mn.View.extend({
  ui: {
    destroy: '.destroy-btn'
  },

  behaviors: {
    DestroyWarn: {
      message: 'you are destroying all your data is now gone!'
    },
    ToolTip: {
      text: 'what a nice mouse you have'
    }
  }
});

Now let's create the DestroyWarn Behavior.

var Mn = require('backbone.marionette');

var DestroyWarn = Mn.Behavior.extend({
  // You can set default options
  // just like you can in your Backbone Models.
  // They will be overridden if you pass in an option with the same key.
  defaults: {
    message: 'You are destroying!'
  },

  // Behaviors have events that are bound to the views DOM.
  events: {
    'click @ui.destroy': 'warnBeforeDestroy'
  },

  warnBeforeDestroy: function() {
    alert(this.options.message);
    // Every Behavior has a hook into the
    // view that it is attached to.
    this.view.destroy();
  }
});

And onto the Tooltip behavior.

var Mn = require('backbone.marionette');

var ToolTip = Mn.Behavior.extend({
  ui: {
    tooltip: '.tooltip'
  },

  onRender: function() {
    this.ui.tooltip.tooltip({
      text: this.options.text
    });
  }
});

Behavior Defaults

defaults can be a hash or function to define the default options for your Behavior. The default options will be overridden depending on what you set as the options per Behavior. (This works just like a Backbone.Model.)

Marionette.Behavior.extend({
  defaults: function() {
    return {
      'deepSpace': 9
    }
  }
});
Marionette.Behavior.extend({
  defaults: {
    'dominion': 'invasion',
    'doge': 'amaze'
  }
});

view

The view is a reference to the View instance that the Behavior is attached to.

Marionette.Behavior.extend({
  handleDestroyClick: function() {
    this.view.destroy();
  }
});

Live example

Nesting Behaviors

In addition to extending a View with Behavior, a Behavior can itself use
other Behaviors. The syntax is identical to that used for a View:

var Mn = require('backbone.marionette');

var Modal = Mn.Behavior.extend({
  behaviors: {
    DestroyWarn: {
      message: 'Whoa! You sure about this?'
    }
  }
});

Live example

Nested Behaviors act as if they were direct Behaviors of the parent Behavior's
view instance.

View Proxy

The Behavior class provides proxies for a selection of View functionality.
This includes listening to events on the view, being able to handle events on
models and collections, and being able to directly interact with the attached
template.

Listening to View Events

Behaviors are powered by an event proxy. This means that any events that are
triggered on a View are passed to all attached behaviors. This includes:

These handlers work exactly as they do on View -
see the View documentation

Events triggered in the behavior instance are not executed in the view. To notify
the view, the behavior must trigger an event in its view property, e.g, this.view.trigger('my:event')

Proxy Handlers

Behaviors provide proxies to a number of the view event handling attributes
including:

Events / Initialize Order

If both view and behavior are listening for the same event, this will be executed
first in the view then in the behavior as below.

The View + Behavior initialize process is as follows:

  1. View is constructed
  2. Behavior is constructed
  3. Behavior is initialized with view property set
  4. View is initialized

This means that the behavior can access the view during its own initialize method.
The view initialize is called later with the information eventually injected by the behavior.

Live example

Using ui

As in views, events and triggers can use the ui references in their
listeners. For more details, see the ui documentation for views.
These can be defined on either the Behavior or the View:

var Mn = require('backbone.marionette');

var MyBehavior = Mn.Behavior.extend({
  ui: {
    saveForm: '.btn-save'
  },

  events: {
    'click @ui.saveForm': 'saveForm'
  },

  modelEvents: {
    invalid: 'showError'
  },

  saveForm: function() {
    this.view.model.save();
  },

  showError: function() {
    alert('You have errors');
  }
});

Live example

If your ui keys clash with keys on the attached view, references within the
behavior will always use the definition on the behavior itself. As views are
only peripherally aware of their behaviors, their ui keys will not be changed
when accessed within the View. For example:

var Mn = require('backbone.marionette');

var MyBehavior = Mn.Behavior.extend({
  ui: {
    saveForm: '.btn-save'
  },

  events: {
    'click @ui.saveForm': 'saveForm'  // .btn-save
  },

  saveForm: function() {
    this.view.model.save();
  }
});

var FirstView = Mn.View.extend({
  behaviors: [MyBehavior],

  ui: {
    saveForm: '.btn-primary'
  },

  events: {
    'click @ui.saveForm': 'checkForm'  // .btn-primary
  },

  checkForm: function() {
    // ...
  }
});

Live example

View and el

The Behavior has a number of proxies attributes that directly refer to the
related attribute on a view:

In addition, each behavior is able to reference the view they are attached to
through the view attribute:

var Mn = require('backbone.marionette');

var ViewBehavior = Mn.Behavior.extend({
  onRender: function() {
    if (this.view.model.get('selected')) {
      this.$el.addClass('highlight');
    }
    else {
      this.$el.removeClass('highlight');
    }
  }
});

Live example

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