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Marionette.Behavior

A Behavior is an isolated set of DOM / user interactions that can be mixed into any View or another Behavior. Behaviors allow you to blackbox View-specific interactions into portable logical chunks, keeping your Views simple and your code DRY.

Documentation Index

The Motivation

As you build more and more complex Views, you will find that your View becomes less about displaying model data, and more about interactions.

These interactions tend to be chunks of logic that you want to use in multiple views.

Usage

Here is an example of a simple ItemView. Let's take a stab at simplifying it, and abstracting Behaviors from it.

var MyView = Marionette.ItemView.extend({
  ui: {
    "destroy": ".destroy-btn"
  },

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

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

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

Interaction points, such as tooltips and warning messages, are generic concepts. There is no need to recode them within your Views. They are prime candidates for abstraction into a higher level, non-coupled concept, which is exactly what Behaviors provide you with.

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

var MyView = Marionette.ItemView.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 DestroyWarn = Marionette.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 ToolTip = Marionette.Behavior.extend({
  ui: {
    tooltip: '.tooltip'
  },

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

Finally, the user must define a location where their Behaviors are stored. Here is a simple example:

  Marionette.Behaviors.behaviorsLookup = function() {
      return window.Behaviors;
  }

In this example, you would then store your Behaviors like this:

window.Behaviors.ToolTip = ToolTip;
window.Behaviors.DestroyWarn = DestroyWarn;

Note that 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 Modal = Marionette.Behavior.extend({
  behaviors: {
    DestroyWarn: {
      message: "Whoa! You sure about this?"
    }
  }
});

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

API

The Event Proxy

Behaviors are powered by an event proxy. This means that any events that are triggered by the view's triggerMethod function are passed to each Behavior on the View as well.

As a real world example, whenever you would define a click event in your View's events hash, you can define the same event listeners and callbacks in the Behavior's events hash. The same follows for modelEvents and collectionEvents. Think of your Behavior as a receiver for all of the events on your View instance.

This concept also allows for a nice decoupled method to communicate to Behaviors from your View instance. You can just call the following from within your View: this.triggerMethod("SomeEvent", {some: "data"}). Then your Behavior class would look like this:

Marionette.Behavior.extend({
    events: {
        'click .foo' : 'onClick'
    },

    onClick: function(data) {
        console.log("wow such data", data);
    }
});

Model Events

modelEvents will respond to the View's model events.

  Marionette.Behavior.extend({
    modelEvents: {
      "change:doge": "onDogeChange"
    },

    onDogeChange: function() {
      // buy more doge...
    }
  });

Collection Events

collectionEvents will respond to the View's collection events.

  Marionette.Behavior.extend({
    collectionEvents: {
      add: "onCollectionAdd"
    },

    onCollectionAdd: function() {
    }
  });

Life Cycle Methods

In addition to providing the same event hashes as Views, Behaviors allow you to use the same life cycle functions that you find on Views. That means methods like initialize, onRender, onBeforeShow, and onBeforeDestroy are all valid as long as the View that implements the Behavior fires the relevant events.

  Marionette.Behavior.extend({

    onRender: function() {
        //Apply a jQuery plugin to every .foo item within the view
        this.$('.foo').bar();
    }
  });

Triggers

Any triggers you define on the Behavior will be triggered in response to the appropriate event on the View.

Marionette.Behavior.extend({
  triggers: {
    'click .label': 'click:label'
  }
});

Grouped Behaviors

The behaviors key allows a Behavior to group multiple behaviors together.

  Marionette.Behavior.extend({
    behaviors: {
      SomeBehavior: {}
    }
  });

$

$ is a direct proxy of the View's $ lookup method.

    Marionette.Behavior.extend({
        onShow: function() {
            this.$('.zerg')
        }
    });

$el and el

el is a direct proxy of the View's el. Similarly, $el is a direct proxy of the View's el cached as a jQuery selector.

Marionette.Behavior.extend({
    onShow: function() {
        this.$el.fadeOut('slow')
    }
});

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();
    }
});

ui

Behaviors can have their own ui hash, which will be mixed into the ui hash of its associated View instance. ui elements defined on either the Behavior or the View will be made available within events and triggers. They also are attached directly to the Behavior and can be accessed within Behavior methods as this.ui.

Marionette.Behavior.extend({
    ui: {
        'foo' : 'li.foo'
    },

    doStuff: function() {
        this.ui.foo.trigger('something');
    }
})
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