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Web Components for Rails.


Do you need an interactive user interface for your Rails application? A cool Rich Client Application with dashboards, portlets and AJAX, Drag&Drop and jQuery?

Is your controller gettin' fat? And your partial-helper-AJAX pile is getting out of control?

Do you want a framework to make the implementation easier? You want Apotomo.

Apotomo is based on Cells, the popular View Components framework for Rails.

It gives you widgets and encapsulation, bubbling events, AJAX page updates, rock-solid testing and more. Check out for more information.


Easy as hell. You just need Ruby 1.9.3/2.0.0 and Rails 3/4.

Add Apotomo to your Gemfile:

gem 'apotomo'


A shitty example is worse than a shitty framework, so let's choose wisely...

Say you had a blog application. The page showing the post should have a comments block, with a list of comments and a form to post a new comment. Submitting should validate and send back the updated comments list, via AJAX.

Let's wrap that comments block in a widget.


Go and generate a widget stub.

rails generate apotomo:widget Comments display write -e haml
create  app/widgets/
create  app/widgets/comments_widget.rb
create  app/widgets/comments/
create  app/widgets/comments/display.html.haml
create  app/widgets/comments/write.html.haml
create  test/widgets/
create  test/widgets/comments_widget_test.rb

Nothing special.

Plug it in

You now tell your controller about the new widget.

class PostsController < ApplicationController

  has_widgets do |root|
    root << widget(:comments, :post => @post)

This creates a widget instance called comments_widget from the class CommentsWidget. We pass the current post into the widget - the block is executed in controller instance context, that's were @post comes from. Handy, isn't it?

Render the widget

Rendering usually happens in your controller view, app/views/posts/show.html.haml, for instance.

%h1= @post.title
  = @post.body
  = render_widget :comments, post: @post

Write the widget

A widget is like a cell which is like a mini-controller.

class CommentsWidget < Apotomo::Widget
  responds_to_event :post

  def display(args)
    @comments = args[:post].comments # the parameter from outside.


Having display as the default state when rendering, this method collects comments to show and renders its view.

And look at line 2 - if encountering a :post event we invoke #post, which is simply another state. How cool is that?

  def post(event)
    @comment = :post_id => event[:post_id]
    @comment.update_attributes event[:comment] # a bit like params[].

    update :state => :display

The event is processed with three steps in our widget:

  • create the new comment
  • re-render the display state
  • update itself on the page

Apotomo helps you focusing on your app and takes away the pain of action dispatching and page updating.

Triggering events

So how and where is the :post event triggered?

Take a look at the widget's view display.html.haml.

= widget_div do
    - for comment in @comments
      %li= comment.text

  = form_for :comment, :url => url_for_event(:post), :remote => true do |f|
    = f.text_field :text
    = f.submit

That's a lot of familiar view code, almost looks like a partial.

As soon as the form is submitted, the form gets serialized and sent using the standard Rails mechanisms. The interesting part here is the endpoint URL returned by #url_for_event as it will trigger an Apotomo event.

Event processing

Now what happens when the event request is sent? Apotomo - again - does three things for you, it

  • accepts the request on a special event route it adds to your app
  • triggers the event in your ruby widget tree, which will invoke the #post state in our comment widget
  • sends back the page updates your widgets rendered

JavaScript Agnosticism

In this example, we use jQuery for triggering. We could also use Prototype, RightJS, YUI, or a self-baked framework, that's up to you.

Also, updating the page is in your hands. Where Apotomo provides handy helpers as #replace, you could also emit your own JavaScript.

Look, replace basically generates

jQuery("comments").replaceWith(<the rendered view>);

If that's not what you want, do

def post(event)
  if event[:comment][:text].explicit?
    render :text => 'alert("Hey, you wanted to submit a pervert comment!");'

Apotomo doesn't depend on any JS framework - you choose!


Apotomo comes with its own test case and assertions to build rock-solid web components.

class CommentsWidgetTest < Apotomo::TestCase
  has_widgets do |root|
    root << widget(:comments, :post => @pervert_post)

  def test_render
    render_widget :comments
    assert_select "li#me"

    trigger :post, :comment => {:text => "Sex on the beach"}
    assert_response 'alert("Hey, you wanted to submit a pervert comment!");'

You can render your widgets, spec the markup, trigger events and assert the event responses, so far. If you need more, let us know!

Using rspec? please check out rspec-apotomo.

Bubbling events

Note: Let's write this paragraph!

Bugs, Community

Please visit, the official project page with lots of examples.

If you have questions, visit us in the IRC channel #cells at

If you wanna be cool, subscribe to our feed!


Copyright (c) 2007-2013 Nick Sutterer

Released under the MIT License.