
View Template Rendering
Unlike Backbone.View, Marionette views provide a customizable solution for rendering a template with data and placing the results in the DOM. import _ from 'underscore';
import { View } from 'backbone.marionette';

const MyView = View.extend({
  tagName: 'h1',
  template: _.template('Contents')
});

const myView = new MyView();
myView.render();
 In the above example the contents of the template attribute will be rendered inside a <h1> tag leeamanda@example.net. Live example 
Documentation Index
 What is a template 
Setting a View Template Using a View Without a Template   
Rendering the Template Using a Custom Renderer Rendering to HTML Rendering to DOM   
Serializing Data Serializing a Model Serializing a Collection Serializing with a CollectionView   
Adding Context Data What is Context Data?    
What is a template?
A template is a function that given data returns either an HTML string or DOM. The default renderer in Marionette expects the template to return an HTML string. Marionette's dependency Underscore comes with an HTML string template compiler. import _ from 'underscore';
import { View } from 'backbone.marionette';

const MyView = View.extend({
  template: _.template('<h1>Hello, world</h1>')
});
 This doesn't have to be an underscore template, you can pass your own rendering function: import Handlebars from 'handlebars';
import { View } from 'backbone.marionette';

const MyView = View.extend({
  template: Handlebars.compile('<h1>Hello, {{ name }}')
});
 Live example 
Setting a View Template
Marionette views use the getTemplate method to determine which template to use for rendering into its el. By default getTemplate is predefined on the view as simply: getTemplate() {
  return this.template
}
 In most cases by using the default getTemplate you can simply set the template on the view to define the view's template, but in some circumstances you may want to set the template conditionally. import { View } from 'backbone.marionette';

const MyView = View.extend({
  template: _.template('Hello World!'),
  getTemplate() {
    if (this.model.has('user')) {
      return _.template('Hello User!');
    }

    return this.template;
  }
});
 Live example 
Using a View Without a Template
By default CollectionView has no defined template and will only attempt to render the template if one is defined. For View there may be some situations where you do not intend to use a template. Perhaps you only need the view's el or you are using prerendered content. In this case setting template to false will prevent the template render. In the case of View it will also prevent the render events. import { View } from 'backbone.marionette';

const MyIconButtonView = View.extend({
  template: false,
  tagName: 'button',
  className: '.icon-button',
  triggers: {
    'click': 'click'
  },
  onRender() {
    console.log('You will never see me!');
  }
});
 
Rendering the Template
Each view class has a renderer which by default passes the view data to the template function and returns the html string it generates. The current default renderer is essentially the following: import { View, CollectionView } from 'backbone.marionette';

function renderer(template, data) {
  return template(data);
}

View.setRenderer(renderer);
CollectionView.setRenderer(renderer);
 Previous to Marionette v4 the default renderer was the TemplateCache. This renderer has been extracted to a separate library: https://github.com/marionettejs/marionette.templatecache and can be used with v4. 
Using a Custom Renderer
You can set the renderer for a view class by using the class method setRenderer. The renderer accepts two arguments. The first is the template passed to the view, and the second argument is the data to be rendered into the template. Here's an example that allows for the template of a view to be an underscore template string. import _ from 'underscore';
import { View } from 'backbone.marionette';

View.setRenderer(function(template, data) {
  return _.template(template)(data);
});

const myView = new View({
  template: 'Hello <%- name %>!',
  model: new Backbone.Model({ name: 'World' })
});

myView.render();

// myView.el is <div>Hello World!</div>
 The renderer can also be customized separately on any extended View. const MyHBSView = View.extend();

// Similar example as above but for handlebars
MyHBSView.setRenderer(function(template, data) {
  return Handlebars.compile(template)(data);
});

const myHBSView = new MyHBSView({
  template: 'Hello {{ name }}!',
  model: new Backbone.Model({ name: 'World' })
});

myHBSView.render();

// myView.el is <div>Hello World!</div>
 Note These examples while functional may not be ideal. If possible it is recommend to precompile your templates which can be done for a number of templating using various plugins for bundling tools such as Browserify or Webpack. 
Rendering to HTML
The default Marionette renders return the HTML as a string. This string is passed to the view's attachElContents method which in turn uses the DOM API's setContents. to set the contents of the view's el with DOM from the string. 
Customizing attachElContents

You can modify the way any particular view attaches a compiled template to the el by overriding attachElContents. This method receives only the results of the view's renderer and is only called if the renderer returned a value. For instance, perhaps for one particular view you need to bypass the DOM API and set the html directly: attachElContent(html) {
  this.el.innerHTML = html;
}
 
Rendering to DOM
Marionette also supports templates that render to DOM instead of html strings by using a custom render. In the following example the template method passed to the renderer will return a DOM element, and then if the view is already rendered utilize morphdom to patch the DOM or otherwise it will set the view's el to the result of the template. (Note in this case the view's el created at instantiation would be overridden). import morphdom from 'morphdom';
import { View } from 'backbone.marionette';

const VDomView = View.extend();

VDomView.setRenderer(function(template, data) {
  const el = template(data);

  if (this.isRendered()) {
    // Patch the view's el contents in the DOM
    morphdom(this.el, el, { childrenOnly: true });
    return;
  }

  this.setElement(el.cloneNode(true));
});
 In this case because the renderer is modifying the el directly, there is no need to return the result of the template rendering for the view to handle in attachElContents. It is certainly an option to return the compiled DOM and modify attachElContents to handle a DOM object instead of a string literal, but in many cases it may be overcomplicated to do so. There are a variety of possibilities for rendering with Marionette. If you are looking into alternatives from the default this may be a useful resource: https://github.com/blikblum/marionette.renderers#renderers 
Serializing Data
Marionette will automatically serialize the data from its model or collection for the template to leeamanda@example.net. You can override this logic and provide serialization of other data with the serializeData method. The method is called with no arguments, but has the context of the view and should return a javascript object for the template to consume. If serializeData does not return data the template may still receive added context or an empty object for rendering. import _ from 'underscore';
import { View } from 'backbone.marionette';

const MyView = View.extend({
  template: _.template(`
    <div><% user.name %></div>
    <ul>
    <% _.each(groups, function(group) { %>
      <li><%- group.name %></li>
    <% }) %>
    </ul>
  `),
  serializeData() {
    // For this view I need both the
    // model and collection serialized
    return {
      user: this.serializeModel(),
      groups: this.serializeCollection(),
    };
  }
});
 Note You should not use this method to add arbitrary extra data to your template. Instead use templateContext to add context data to your template. 
Serializing a Model
If the view has a model it will pass that model's attributes to the template. import _ from 'underscore';
import Backbone from 'backbone';
import { View } from 'backbone.marionette';

const MyModel = Backbone.Model.extend({
  defaults: {
    name: 'world'
  }
});

const MyView = View.extend({
  template: _.template('<h1>Hello, <%- name %></h1>')
});

const myView = new MyView({ model: new MyModel() });
 Live example How the model is serialized can also be customized per view. import _ from 'underscore';
import { View } from 'backbone.marionette';

const MyView = View.extend({
  serializeModel() {
    const data = _.clone(this.model.attributes);

    // serialize nested model data
    data.sub_model = data.sub_model.attributes;

    return data;
  }
});
 
Serializing a Collection
If the view does not have a model but has a collection the collection's models will be serialized to an array provided as an items attribute to the template. import _ from 'underscore';
import Backbone from 'backbone';
import { View } from 'backbone.marionette';

const MyView = View.extend({
  template: _.template(`
    <ul>
    <% _.each(items, function(item) { %>
      <li><%- item.name %></li>
    <% }) %>
    </ul>
  `)
});

const collection = new Backbone.Collection([
  {name: 'Steve'}, {name: 'Helen'}
]);

const myView = new MyView({ collection });
 Live example How the collection is serialized can also be customized per view. import _ from 'underscore';
import { View } from 'backbone.marionette';

const MyView = View.extend({
  serializeCollection() {
    return _.map(this.collection.models, model => {
      const data = _.clone(model.attributes);

      // serialize nested model data
      data.sub_model = data.sub_model.attributes;

      return data;
    });
  }
});
 
Serializing with a CollectionView

if you are using a template with a CollectionView that is not also given a model, your CollectionView will serialize the collection for the template. This could be costly and unnecessary. If your CollectionView has a template it is advised to either use an empty model or override the serializeData method. 
Adding Context Data
Marionette views provide a templateContext attribute that is used to add extra information to your templates. This can be either an object, or a function returning an object. The keys on the returned object will be mixed into the model or collection keys and made available to the template. import _ from 'underscore';
import { View } from 'backbone.marionette';

const MyView = View.extend({
  template: _.template('<h1>Hello, <%- name %></h1>'),
  templateContext: {
    name: 'World'
  }
});
 Additionally context data overwrites the serialized data import _ from 'underscore';
import { View } from 'backbone.marionette';

const MyView = View.extend({
  template: _.template('<h1>Hello, <%- name %></h1>'),
  templateContext() {
    return {
      name: this.model.get('name').toUpperCase()
    };
  }
});
 You can also define a template context value as a method. How this method is called is determined by your templating solution. For instance with handlebars a method is called with the context of the data passed to the template. import Handlebars from 'handlebars';
import Backbone from 'backbone';
import { View } from 'backbone.marionette';

const MyView = View.extend({
  template: Handlebars.compile(`
    <h1{{#if isDr}} class="dr"{{/if}}>Hello {{ fullName }}</h1>,
  `),
  templateContext: {
    isDr() {
      return (this.degree) === 'phd';
    },
    fullName() {
      // Because of Handlebars `this` here is the data object
      // passed to the template which is the result of the
      // templateContext mixed with the serialized data of the view
      return this.isDr() ? `Dr. { this.name }` : this.name;
    }
  }
});

const myView = new MyView({
  model: new Backbone.Model({ degree: 'masters', name: 'Joe' });
});
 Note the data object passed to the template is not deeply cloned and in some cases is not leeamanda@example.net. Take caution when modifying the data passed to the template, that you are not also modifying your model's data indirectly. 
What is Context Data?
While serializing data deals more with getting the data belonging to the view into the template, template context mixes in other needed data, or in some cases, might do extra computations that go beyond simply "serializing" the view's model or collection import _ from 'underscore'
import { CollectionView } from 'backbone.marionette';
import GroupView from './group-view';

const MyCollectionView = CollectionView.extend({
  tagName: 'div',
  childViewContainer: 'ul',
  childView: GroupView,
  template: _.template(`
    <h1>Hello <% name %> of <% orgName %></h1>
    <div>You have <% stats.public %> group(s).</div>
    <div>You have <% stats.private %> group(s).</div>
    <h3>Groups:</h3>
    <ul></ul>
  `),
  templateContext() {
    const user = this.model;
    const organization = user.getOrganization();
    const groups = this.collection;

    return {
      orgName: organization.get('name'),
      name: user.getFullName(),
      stats: groups.countBy('type')
    };
  }
})


    
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