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Common Backbone.js usage patterns.

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README.md

Backbone patterns

This is a document with best practices in Backbone. This is a massive work-in-progress.

This document assumes that you already have some knowledge of Backbone.js, jQuery, and of course, JavaScript itself.

Model patterns

Preloading collections

The problem: Your application needs models to be available on page load.

Solution: Preload model instances by creating collections on page load.

Define collections

Define your collections as an inline script in the HTML file. If you have collections for Photos, you may be doing it this way:

  <body>
    ...

    <script>
      App.photos = new Photos([
        { id: 2, name: "My dog", filename: "IMG_0392.jpg" },
        { id: 3, name: "Our house", filename: "IMG_0393.jpg" },
        { id: 4, name: "My favorite food", filename: "IMG_0394.jpg" },
        { id: 5, name: "His bag", filename: "IMG_0394.jpg" },
        ...
      ]);
    </script>
  </body>

Accessing instances

To get a single Photo, instead of creating a Photo instance and using fetch(), simply pluck it from the giant collection.

// Gets by ID
var photo = App.photos.get(2);

// Gets a bunch of photos based on criteria
var photo = App.photos.select(function(photo) {
  return photo.filename.match(/^IMG/);
});

In Ruby (ERB)

In your server-side templates, you will probably be using to_json on a collection of your server-side models.

<script>
  App.photos = new Photos(<%= @photos.to_json %>);
</script>

In Ruby (HAML)

If you use HAML, you will need use a syntax similar to this.

:javascript
  != "App.photos = new Photos(#{@photos.to_json});"

In PHP

In your server-side templates, you will probably be using json_encode() on a collection of your server-side models.

<script>
  App.photos = new Photos(<?php echo json_encode($photos); ?>);
</script>

View patterns

Inline views

The problem: if you need to use view templates in a small Backbone application, defining your templates in JavaScript code will be unwieldy and difficult to maintain.

Solution: You may need some view templates to be inline in the HTML page.

This solution has been outlined by John Resig in his blog post about JavaScript micro templating.

Defining inline views

You can put views in an HTML <script> tag.

  • Change the type attribute to something else so it will not be interpreted as JavaScript.

  • Set an id so we can easily refer to it.

<script type="text/html" id="foo">
  <div class='contact'>
    <strong><%= name %></strong>
    <span><%= email %></span>
  </div>
</script>

Using inline views

In JavaScript, you can get the innerText of that HTML element to fetch the raw template data. You can pass this onto Underscore's _.template to create a template function.

$("#foo").text();
//=> "<div class='contact'>\n<strong><%= name %></str..."

template = _.template($("#foo").text());
//=> function() { ... }

Integrating into Backbone

In practice, you will most likely be using this in the render() method of a view like so.

ContactView = Backbone.View.extend({
  template: function() {
    var template = _.template($("#foo").text());
    return template.apply(this, arguments);
  },

  render: function() {
    // This is a dictionary object of the attributes of the models.
    // => { name: "Jason", email: "j.smith@gmail.com" }
    var dict = this.model.toJSON();

    // Pass this object onto the template function.
    // This returns an HTML string.
    var html = this.template(hash);

    // Append the result to the view's element.
    $(this.el).append(html);

    // ...
  }
})

Limitations

Single-page apps only. This assumes that your Backbone application is all contained in one HTML page. If your app spans across multiple HTML pages, and each page will be needing the same templates, you may be redundantly streaming the template data to the browser uneededly. Consider using JST templates instead.

JST templates

The problem: if you need to use view templates in a small-to-large Backbone application, defining your templates in JavaScript code will be unwieldy and difficult to maintain.

Solution: You may need put the templates in a JavaScript file.

The structure

Your app will need to serve a dynamically-created JavaScript file that compiles your files.

A common JST file will create the JST object (in the window namespace), with each of it's members defined as template functions. In this example, we'll use Underscore's _.template, which returns functions.

// http://myapp.com/javascripts/jst.js
window.JST = {};

window.JST['person/contact'] = _.template(
    "<div class='contact'><%= name %> ..."
);

window.JST['person/edit'] = _.template(
    "<form method='post'><input type..."
);

You will then need to link to this JavaScript page in your HTML.

<script src="http://myapp.com/javascripts/jst.js"></script>

Using JST templates

In your JavaScript code, simply access the JST object's members to access the views.

var html = JST['person/edit']();

var dict = { name: "Jason", email: "j.smith@gmail.com" };
var html = JST['person/contact'](dict);

Integration notes

  • Rails 3.1: Sprockets already comes with support for JST pages.
  • Rails 3.0 and below: consider using Sprockets an Jammit.
  • In Sinatra: The sinatra-backbone gem can take care of dynamically serving JST templates.

Partials

The problem: there may be parts of HTML templates that can be reused in many parts of the application. Defining them more than once is not DRY, which may make your application less maintainable.

Solution: separating these snippets into partials.

Partials are templates that are meant to be used inside other templates.

One typical use of partials is for lists where the template for list items may be defined as a separate template from the list itself.

Solution

You can pass the template function for the partial as a parameter to the first template.

In this example, the function itemTemplate is passed onto the parameters for template().

TasksList = Backbone.View.extend({
  template: _.template("
    <ul class='task_list'>
      <% items.each(function(item) { %>
        <%= itemTemplate(item) %>
      <% }); %>
    </ul>
  "),

  itemTemplate: _.template("
    <li><%= name %></li>
  "),

  render: function() {
    var html = this.template({
      items: tasks /* a collection */,
      itemTemplate: this.itemTemplate
    });

    $(this.el).append(html);
  }
});

Animation buffer

The problem: When you have events that trigger animations, they can mess up when the user clicks to fast.

The solution: Make a buffering system to ensure that animations are fired serially (one after the other) and never parallel (at the same time).

The situation

Let's say you have this innocent code that performs an animation.

One fundamental flaw here is that it assumes that .next() will only be called when it is not animating. When the user clicks "Next" while the animation is working, unexpected results will occur.

PicturesView = Backbone.View.extend({
  events: {
    'click .next':     'next'
  },

  next: function() {
    var current = this.$(".current");
    var next    = this.$(".current + div");

    if (next.length == 0) { return; }

    // Make the current one move to the left via jQuery.
    // This uses jQuery.fn.animate() that changes CSS values, then fires
    // the function supplied when it's done.
    current.animate({ left: -300, opacity: 0 }, function() {
      current.removeClass('.current');
      next.addClass('.current');
    });
  }
});

The solution

Here's a simple buffering solution. It provides two commands:

  • add(fn) which adds a given function to the buffer, and
  • next() which moves onto the next command.

To use this, put your animations inside an anonymous function to be passed onto add(). Be sure to trigger next() when the animations are done.

Buffer = {
  commands: [],

  // Adds a command to the buffer, and executes it if it's the only command
  // to be ran.
  add: function(fn) {
    this.commands.push(fn);
    if (this.commands.length == 1) this.next();
  },

  // Moves onto the next command in the buffer.
  next: function() {
    if (this.commands.length) this.commands.shift()();
  }
};

Example

This is our example from a while ago that has been modified to use the bufferer.

next: function() {
  var current = this.$(".current");
  var next    = this.$(".current + div");

  if (next.length == 0) { return; }

  // Ensure that the animation will not happen while another animation is
  // ongoing.
  Buffer.add(function() {
    current.animate({ left: -300, opacity: 0 }, function() {
      current.removeClass('.current');
      next.addClass('.current');

      // Trigger the next animation.
      Buffer.next();
    });
  });
}

Conventions

Naming convention

Classes often start in uppercase letters, while instances start with lowercase letters. This is a throwback of the general Python and Ruby practice of naming constants as uppercase camel.

// Classes:
Photo
Album
Author

// Instances:
photo
myAlbum

For names with multiple words, JavaScript often calls for CamelCase. Using underscores are often discouraged, considering most JavaScript libraries already use CamelCase.

// Good:
PhotoAlbum
albumCover

// Avoid:
photo_album
album_cover

Namespace convention

The convention we use puts everything in one App namespace to keep things organized properly.

window.App = {
    ...
};

Subsequent models, views, and other classes will be made in this namespace.

App.Photo = Backbone.Model.extend({
    ...
};

Some people prefer to use namespaces based on their app's name. Consider, say, BF.Photo (instead of App.Photo) if your application name is "Bacefook."

Models:                    App.Photo
Collections:               App.Photos
Views:                     App.PhotoView
Main router:               App.Router
Custom routers:            App.SpecialRouter

Router instance:           App.router
View instances:            App.photoView
Singleton model instances: App.photo
Collection instances:      App.photos

Variation: two-level namespace

Some people prefer a verbose two-level version where the classes are divided ino their own namespaces as well.

This is often done to make it easy to iterate over all available models, collections, and views.

Models:                    App.Models.Photo
Collections:               App.Collections.Photos
Views:                     App.Views.Photo

Variation: Classes in global

Some prefer to have classes in the global namespace. This makes typing them out easy: you can use new Photo instead of new App.Photo.

Models:                    window.Photo
Collections:               window.Photos
Views:                     window.PhotoView
Main router:               window.Router
Custom routers:            window.SpecialRouter

File naming

Most applications always seem to have 3 basic JavaScript files.

The main namespace

This is often app.js, which defines the basic namespace.

// app.js
window.App = {
    ...
};

The individual classes

If you use the namespacing method outlined earlier in this document, there are 2 popular naming conventions for individual classes:

  • Name the files as the exact class name they contain. For instance, App.PhotoView should be stored as app/photoview.js.

  • Place each of the class types in their own folders. For instance, the PhotoView may be defined as app/views/photoview.js, or views/photoview.js.

In this approach, avoid putting code in the files other than the actual class it defines. This makes your convention predictable for the benefit of those new to your project.

// app/photoview.js
App.PhotoView = Backbone.View.extend({
    ...
});

The setup/glue code file

This is the file where you do miscellaneous things that do not belong in any of the Backbone classes:

  • Instanciate the default view
  • Initialize the Backbone Router
  • Provide options for jQuery and it's plugins

This is often named application.js or setup.js.

In larger projects, this can span multiple files. Don't be afraid to refactor it to multiple files.

This is often the only place you will want to put the onload hook $(function() { ... }).

$(function() {
  // Set up some options for jQuery and plugins.
  $(document).ajaxError(function() {
    alert("There was an error.");
  });

  // Provide options for your plugins.
  $("a[rel~=lightbox]").click(function() {
    $(this).openAsLightbox();
  });

  Backbone.emulateJSON = true;

  // Initialize Backbone views.
  App.chromeView = new App.ChromeView({ el: $("body") });
  App.router = new App.Router;

  // Initialize the Backbone router.
  Backbone.history.start();
});

Load order

Consider loading them in this order:

  • app.js (the namespace)
  • app/*.js (individual classes)
  • setup.js (the glue)
<script src="javascripts/app.js"></script>
<script src="javascripts/app/photo.js"></script>
<script src="javascripts/app/photoview.js"></script>
<script src="javascripts/app/photos.js"></script>
<script src="javascripts/setup.js"></script>

Anti-patterns

Things NOT to do!

$() abuse

Some people like putting things in jQuery's $(function() { .. }) to defer execution until the DOM is ready. Don't do it unless you have to.

// AVOID this!
$(function() {
  App.PhotoView = Backbone.View.extend({
    ...
  });
});

Things outside views

Put things in your view class code as much as possible.

Event handlers outside views

Every time you make an event handler outside a view class, consider making a new view class.

App.PhotoView = Backbone.View.extend({
  ...
});

// AVOID this!
$("a.photo").click(function() { ... });

Acknowledgements

© 2011, Rico Sta. Cruz. Released under the MIT License.

This document is authored and maintained by Rico Sta. Cruz with help from it's contributors. It is sponsored by my startup, Sinefunc, Inc.

To do list

  • Model associations
  • View modes
  • Nested views
  • Router entry/exit
  • View helpers
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