TodoMVC Tutorial Part I

Prerequisites
Linux or Mac system
(Android, ChromeOS and Windows are not supported)
Ruby on Rails must be installed: https://rubyonrails.org/​
NodeJS must be installed: https://nodejs.org​
Yarn must be installed: https://yarnpkg.com/en/docs/install​
The goals of this tutorial
In this tutorial, you will build the classic TodoMVC application using Hyperstack. This tutorial will demonstrate several key Hyperstack concepts - client side Components and Isomorphic Models.
The finished application will
1.have the ability to add and edit todos;
2.be able change the complete/incomplete state;
3.filter the list of displayed todos to show all, complete, or incomplete (active) todos;
4.have html5 history so that as the filter changes so does the URL;
5.have server side persistence;
6.and synchronization across multiple browser windows.
You will write less than 100 lines of code, and the tutorial should take about 1-2 hours to complete.
Skills required
Basic knowledge of Ruby is needed, knowledge of Ruby on Rails is helpful.
Chapter 1: Setting Things Up
First you need to create a new project for this tutorial.
rails new todo-demo --skip-test
This command will create a new Rails project.
Caution: you can name the app anything you want, we recommend todo-demo, but whatever you do DON'T call it todo, as this name will be needed later!
Now
cd todo-demo
which will change the working directory to your new todo rails project.
Now run
bundle add 'rails-hyperstack' --version "~> 1.0.alpha1.0"
which will install the rails-hyperstack 'gem' into the system.
Once the gem is installed run
bundle exec rails hyperstack:install
to complete the hyperstack installation.
Finally find the config/initializers/hyperstack.rb file, and make sure that this line is not commented out:
Hyperstack.import 'hyperstack/component/jquery', client_only: true
Ignore any comments saying that it should be commented out, this is a typo in the current installer
Start the Rails app
In the console run the following command to start the Rails server and Hotloader.
bundle exec foreman start
For the rest of the tutorial you will want to keep foreman running in the background and have a second console window open in the todo-demo directory to execute various commands.
Navigate to http://localhost:5000/ in your browser and you should see the word Hello world from Hyperstack! displayed on the page. Hyperstack will need a moment to start and pre-compile with the first request.
Note: you will be using port 5000 not the more typical 3000, this is because of the way the Hotloader is configured.
Make a Simple Change
Bring up your favorite editor on the todo-demo directory. You will see folders like app, bin, config and db. These have all been preinitialized by Rails and Hyperstack gems.
Now find the app/hyperstack/components/app.rb file. It looks like this:
# app/hyperstack/component/app.rb
​
# This is your top level component, the rails router will
# direct all requests to mount this component.  You may
# then use the Route psuedo component to mount specific
# subcomponents depending on the URL.
​
class App < HyperComponent
  include Hyperstack::Router
​
  # define routes using the Route psuedo component.  Examples:
  # Route('/foo', mounts: Foo)                : match the path beginning with /foo and mount component Foo here
  # Route('/foo') { Foo(...) }                : display the contents of the block
  # Route('/', exact: true, mounts: Home)     : match the exact path / and mount the Home component
  # Route('/user/:id/name', mounts: UserName) : path segments beginning with a colon will be captured in the match param
  # see the hyper-router gem documentation for more details
​
  render do
    H1 { "Hello world from Hyperstack!" }
  end
end
Change the string displayed to something like: "Todo App Coming Soon". You will see the display instantly change when you save the file.
You can also delete the comments as we will go over details of routing later.
The Hyperstack UI is built from components. Each component is defined by a subclass of HyperComponent. In some cases there will only be one instance of the class displayed, and as we will see at other times the class is reused to display multiple components. If you are familiar with Rails or the MVC structure then you can think of Components as views that continuously update as the state of the application changes.
Chapter 2:  Hyperstack Models are Rails Models
We are going to add our Todo Model, and discover that Hyperstack models are in fact Rails ActiveRecord models.
You can access your rails models on the client using the same syntax you use on the server.
Changes on the client are mirrored on the server.
Changes to models on the server are synchronized with all participating browsers.
Data access is protected by a robust policy mechanism.
A Rails ActiveRecord Model is a Ruby class that is backed by a database table. In this example we will have one model class called Todo. When manipulating models, Rails automatically generates the necessary SQL code for you. So when Todo.all is evaluated Rails generates the appropriate SQL and turns the result of the query into appropriate Ruby data structures.
Hyperstack Models are extensions of ActiveRecord Models that synchronize the data between the client and server automatically for you. So now Todo.all can be evaluated on the server or the client.
Okay lets see it in action:
1.Add the Todo Model:
As stated earlier we keep foreman running in the first console and open a second console. In this second console window run on a single line:
bundle exec rails g model Todo title:string completed:boolean priority:integer
This runs a Rails generator which will create the skeleton Todo model class, and create a migration which will add the necessary tables and columns to the database.
Now look in the db/migrate/ directory, and edit the migration file you have just created. The file will be titled with a long string of numbers then "create_todos" at the end. Change the line creating the completed boolean field so that it looks like this:
...
t.boolean :completed, null: false, default: false
...
For details on 'why' see this blog post. Basically this insures completed is treated as a real boolean, and will avoid having to check between false and null later on.
Now run:
bundle exec rails db:migrate
which will create the table.
1.Make Your Model Public:
Move models/todo.rb to hyperstack/models
This will make the model accessible on the clients and the server, subject to any data access policies.
Note: The hyperstack installer adds a policy that gives full permission to all clients but only in development and test modes. Have a look at app/policies/application_policy if you are interested.
1.Try It:
Now change your App component's render method to:
class App < HyperComponent
  include Hyperstack::Router
  render do
    H1 { "Number of Todos: #{Todo.count}" }
  end
end
You will now see Number of Todos: 0 displayed.
Now start a rails console
bundle exec rails c
and type:
Todo.create(title: 'my first todo')
This will create a new Todo in the server's database, which will cause your Hyperstack application to be updated and you will see the count change to 1!
Try it again:
Todo.create(title: 'my second todo')
and you will see the count change to 2!
Are we having fun yet? I hope so! As you can see Hyperstack is synchronizing the Todo model between the client and server. As the state of the database changes, Hyperstack buzzes around updating whatever parts of the DOM were dependent on that data (in this case the count of Todos).
Notice that we did not create any APIs to achieve this. Data on the server is synchronized with data on the client for you.
Chapter 3: Creating the Top Level App Structure
Now that we have all of our pieces in place, lets build our application.
Replace the entire contents of app.rb with:
# app/hyperstack/components/app.rb
class App < HyperComponent
  include Hyperstack::Router
  render(SECTION) do
    Header()
    Index()
    Footer()
  end
end
After saving you will see the following error displayed:
Uncaught error: Header: undefined method `Header' for # in App (created by Hyperstack::Internal::Component::TopLevelRailsComponent) in Hyperstack::Internal::Component::TopLevelRailsComponent
because we have not defined the three subcomponents. Lets define them now:
Add three new ruby files to the app/hyperstack/components folder:
# app/hyperstack/components/header.rb
class Header < HyperComponent
  render(HEADER) do
    'Header will go here'
  end
end
# app/hyperstack/components/index.rb
class Index < HyperComponent
  render(SECTION) do
    'List of Todos will go here'
  end
end
# app/hyperstack/components/footer.rb
class Footer < HyperComponent
  render(DIV) do
    'Footer will go here'
  end
end
Once you add the Footer component you should see:
Header will go here List of Todos will go here Footer will go here </div>
If you don't, restart the server (foreman in the first console), and reload the browser.
Notice how the usual HTML tags such as DIV, SECTION, and HEADER are all available as well as all the other HTML and SVG tags.
Hyperstack uses the following conventions to easily distinguish between HTML tags, application defined components and other helper methods:
HTML tags are in all caps
Application components are CamelCased
other helper methods are snake_cased
Chapter 4: Listing the Todos, Hyperstack Params, and Prerendering
To display each Todo we will create a TodoItem component that takes a parameter:
# app/hyperstack/components/todo_item.rb
class TodoItem < HyperComponent
  param :todo
  render(LI) do
    todo.title
  end
end
We can use this component in our Index component:
# app/hyperstack/components/index.rb
class Index < HyperComponent
  render(SECTION) do
    UL do
      Todo.each do |todo|
        TodoItem(todo: todo)
      end
    end
  end
end
Now you will see something like
Header will go here Footer will go here </div>
As you can see components can take parameters (or props in react.js terminology.)
Rails uses the terminology params (short for parameters) which have a similar purpose to React props, so to make the transition more natural for Rails programmers Hyperstack uses params, rather than props.
Params are declared using the param macro which creates an accessor method of the same name within the component.
Our Index component mounts a new TodoItem with each Todo record and passes the Todo to the TodoItem component as the parameter.
Now go back to Rails console and type
Todo.last.update(title: 'updated todo')
and you will see the last Todo in the list changing.
Try adding another Todo using create like you did before. You will see the new Todo is added to the list.
Chapter 5: Adding Inputs to Components
So far we have seen how our components are synchronized to the data that they display. Next let's add the ability for the component to change the underlying data.
First add an INPUT html tag to your TodoItem component like this:
# app/hyperstack/components/todo_item.rb
class TodoItem < HyperComponent
  param :todo
  render(LI) do
    INPUT(type: :checkbox, checked: todo.completed)
    todo.title
  end
end
You will notice that while it does display the checkboxes, you can not change them by clicking on them.
For now we can change them via the console like we did before. Try executing
Todo.last.update(completed: true)
and you should see the last Todo's completed checkbox changing state.
To make our checkbox input change its own state, we will add an event handler for the change event:
# app/hyperstack/components/todo_item.rb
class TodoItem < HyperComponent
  param :todo
  render(LI) do
    INPUT(type: :checkbox, checked: todo.completed)
    .on(:change) { todo.update(completed: !todo.completed) }
    todo.title
  end
end
It reads like a good novel doesn't it? On the change event update the todo, setting the completed attribute to the opposite of its current value. The rest of coordination between the database and the display is taken care of for you by the Hyperstack.
After saving your changes you should be able change the completed state of each Todo, and check on the rails console (say by checking Todo.last.completed) and you will see that the value has been persisted to the database. You can also demonstrate this by refreshing the page.
We will finish up by adding a delete link at the end of the Todo item:
# app/hyperstack/components/todo_item.rb
class TodoItem < HyperComponent
  param :todo
  render(LI) do
    INPUT(type: :checkbox, checked: todo.completed)
    .on(:change) { todo.update(completed: !todo.completed) }
    SPAN { todo.title } # See note below...
    A { ' -X-' }.on(:click) { todo.destroy }
  end
end
Note: If a component or tag block returns a string it is automatically wrapped in a SPAN, to insert a string in the middle you have to wrap it a SPAN like we did above.
I hope you are starting to see a pattern here. Hyperstack components determine what to display based on the state of some objects. External events, such as mouse clicks, the arrival of new data from the server, and even timers update the state. Hyperstack recomputes whatever portion of the display depends on the state so that the display is always in sync with the state. In our case the objects are the Todo model and its associated records, which have a number of associated internal states.
By the way, you don't have to use Models to have states. We will see later that states can be as simple as boolean instance variables.
Chapter 6: Routing
Now that Todos can be completed or active, we would like our user to be able display either "all" Todos, only "completed" Todos, or "active" (or incomplete) Todos. We want our URL to reflect which filter is currently being displayed. So /all will display all todos, /completed will display the completed Todos, and of course /active will display only active (or incomplete) Todos. We would also like the root url / to be treated as /all
To achieve this we first need to be able to scope (or filter) the Todo Model. So let's edit the Todo model file so it looks like this:
# app/hyperstack/models/todo.rb
class Todo < ApplicationRecord
  scope :completed, -> { where(completed: true)  }
  scope :active,    -> { where(completed: false) }
end
Now we can say Todo.all, Todo.completed, and Todo.active, and get the desired subset of Todos. You might want to try it now in the rails console.
Note: you will have to do a reload! to load the changes to the Model.
We would like the URL of our App to reflect which of these filters is being displayed. So if we load
/all we want the Todo.all scope to be run;
/completed we want the Todo.completed scope to be run;
/active we want the Todo.active scope to be run;
/ (by itself) then we should redirect to /all.
Having the application display different data (or whole different components) based on the URL is called routing.
Lets change App to look like this:
# app/hyperstack/components/app.rb
class App < HyperComponent
  include Hyperstack::Router
  render(SECTION) do
    Header()
    Route('/', exact: true) { Redirect('/all') }
    Route('/:scope', mounts: Index)
    Footer()
  end
end
and the Index component to look like this:
# app/hyperstack/components/index.rb
class Index < HyperComponent
  include Hyperstack::Router::Helpers
  render(SECTION) do
    UL do
      Todo.send(match.params[:scope]).each do |todo|
        TodoItem(todo: todo)
      end
    end
  end
end
Lets walk through the changes:
We mount the Header components as before.
We then check to see if the current route exactly matches / and if it does, redirect to /all.
Then instead of directly mounting the Index component, we route to it based on the URL.  In this case if the url must look like /xxx.
Index now includes (mixes-in) the Hyperstack::Router::Helpers module which has methods like match.
Instead of simply enumerating all the Todos, we decide which scope to filter using the URL fragment matched by :scope.  
Notice the relationship between Route('/:scope', mounts: Index) and match.params[:scope]:
During routing each Route is checked. If it matches then the indicated component is mounted, and the match parameters are saved for that component to use.
You should now be able to change the url from /all, to /completed, to /active, and see a different set of Todos. For example if you are displaying the /active Todos, you will only see the Todos that are not complete. If you check one of these it will disappear from the list.
Rails also has the concept of routing, so how do the Rails and Hyperstack routers interact? Have a look at the config/routes.rb file. You will see a line like this: get '/(*other)', to: 'hyperstack#app' This is telling Rails to accept all requests and to process them using the Hyperstack controller, which will attempt to mount a component named App in response to the request. The mounted App component is then responsible for further processing the URL.
For more complex scenarios Hyperstack provides Rails helper methods that can be used to mount components from your controllers, layouts, and views.
Chapter 7:  Helper Methods, Inline Styling, Active Support and Router Nav Links
Of course we will want to add navigation to move between these routes. We will put the navigation in the footer:
# app/hyperstack/components/footer.rb
class Footer < HyperComponent
  def link_item(path)
    A(href: "/#{path}", style: { marginRight: 10 }) { path.camelize }
  end
  render(DIV) do
    link_item(:all)
    link_item(:active)
    link_item(:completed)
  end
end
Save the file, and you will now have 3 links, that you will change the path between the three options.
Here is how the changes work:
Hyperstack is just Ruby, so you are free to use all of Ruby's rich feature set to structure your code.
For example the link_item method is just a helper method to save us some typing.
The link_item method uses the path argument to construct an HTML Anchor tag.
Hyperstack comes with a large portion of the Rails active-support library.
For the text of the anchor tag we use the active-support method camelize.
Later we will add proper css classes, but for now we use an inline style.
Notice that the css margin-right is written marginRight, and that 10px can be expressed as the integer 10.
Notice that as you click each link the page reloads. However what we really want is for the links to simply change the route, without reloading the page.
To make this happen we will mixin some router helpers by including HyperRouter::ComponentMethods inside of class.
Then we can replace the anchor tag with the Router's NavLink component:
Change
A(href: "/#{path}", style: { marginRight: 10 }) { path.camelize }
to
NavLink("/#{path}", style: { marginRight: 10 }) { path.camelize }
# note that there is no href key in NavLink
Our component should now look like this:
# app/hyperstack/components/footer.rb
class Footer < HyperComponent
  include Hyperstack::Router::Helpers
  def link_item(path)
    NavLink("/#{path}", style: { marginRight: 10 }) { path.camelize }
  end
  render(DIV) do
    link_item(:all)
    link_item(:active)
    link_item(:completed)
  end
end
After this change you will notice that changing routes does not reload the page, and after clicking to different routes, you can use the browsers forward and back buttons.
How does it work? The NavLink component reacts to a click just like an anchor tag, but instead of changing the window's URL directly, it updates the HTML5 history object. Associated with this history is (hope you guessed it) state. So when the history changes it causes any components depending on the state of the URL to be re-rendered.
Chapter 8: Create a Basic EditItem Component
So far we can mark Todos as completed, delete them, and filter them. Now we create an EditItem component so we can change the Todo title.
Add a new component like this:
# app/hyperstack/components/edit_item.rb
class EditItem < HyperComponent
  param :todo
  render do
    INPUT(defaultValue: todo.title)
    .on(:enter) do |evt|
      todo.update(title: evt.target.value)
    end
  end
end
Before we use this component let's understand how it works.
It receives a todo param which will be edited by the user;
The title of the todo is displayed as the initial value of the input;
When the user types the enter key the todo is updated.
Now update the TodoItem component replacing
SPAN { todo.title }
with
EditItem(todo: todo)
Try it out by changing the text of some our your Todos followed by the enter key. Then refresh the page to see that the Todos have changed.
Chapter 9: Adding State to a Component, Defining Custom Events, and a Lifecycle Callback.
This all works, but it's hard to use. There is no feedback indicating that a Todo has been saved, and there is no way to cancel after starting to edit. We can make the user interface much nicer by adding state (there is that word again) to the TodoItem. We will call our state editing. If editing is true, then we will display the title in a EditItem component, otherwise we will display it in a LABEL tag. The user will change the state to editing by double clicking on the label. When the user saves the Todo, we will change the state of editing back to false. Finally we will let the user cancel the edit by moving the focus away (the blur event) from the EditItem. To summarize:
User double clicks on any Todo title: editing changes to true.
User saves the Todo being edited: editing changes to false.
User changes focus away (blur) from the Todo being edited: editing changes to false.
In order to accomplish this our EditItem component is going to communicate to its parent via two application defined events - saved and cancel.
Add the following 5 lines to the EditItem component like this:
# app/hyperstack/components/edit_item.rb
class EditItem < HyperComponent
  param :todo
  fires :saved                               # add
  fires :cancel                              # add
  after_mount { jQ[dom_node].focus }         # add
​
  render do
    INPUT(defaultValue: todo.title)
    .on(:enter) do |evt|
      todo.update(title: evt.target.value)
      saved!                                 # add
    end
    .on(:blur) { cancel! }                   # add
  end
end
The first two new lines add our custom events which will be fired by the component.
The next new line uses one of several Lifecycle Callbacks. In this case we need to move the focus to the EditItem component after it is mounted. The jQ method is Hyperstack's jQuery wrapper, and dom_node is the method that returns the actual dom node where this instance of the component is mounted. This is the INPUT html element as defined in the render method.
The saved! line will fire the saved event in the parent component. Notice that the method to fire a custom event is the name of the event followed by a bang (!).
Finally we add the blur event handler and fire our cancel event.
Now we can update our TodoItem component to react to three events: double_click, saved and cancel.
# app/hyperstack/components/todo_item.rb
class TodoItem < HyperComponent
  param :todo
  render(LI) do
    if @editing
      EditItem(todo: todo)
      .on(:saved, :cancel) { mutate @editing = false }
    else
      INPUT(type: :checkbox, checked: todo.completed)
      .on(:change) { todo.update(completed: !todo.completed) }
      LABEL { todo.title }
      .on(:double_click) { mutate @editing = true }
      A { ' -X-' }
      .on(:click) { todo.destroy }
    end
  end
end
All states in Hyperstack are simply Ruby instance variables (ivars for short which are variables with a leading @). Here we use the @editing ivar.
We have already used a lot of states that are built into the HyperModel and HyperRouter. The states of these components are built out of collections of instance variables like @editing.
In the TodoItem component the value of @editing controls whether to render the EditItem or the INPUT, LABEL, and Anchor tags.
Because @editing (like all ivars) starts off as nil, when the TodoItem first mounts, it renders the INPUT, LABEL, and Anchor tags. Attached to the label tag is a double_click handler which does one thing: mutates the component's state setting @editing to true. This then causes the component to re-render, and now instead of the three tags, we will render the EditItem component.
Attached to the EditItem component is the saved and cancel handler (which is shared between the two events) that mutates the component's state, setting @editing back to false.
Using and changing state in a component is as simple as reading or changing the value of some instance variables. The only caveat is that whenever you want to change a state variable whether it's a simple assignment or changing the internal value of a complex structure like a hash or array you use the mutate method to signal Hyperstack that that state is changing.
Chapter 10: Using EditItem to create new Todos
Our EditItem component has a good robust interface. It takes a Todo, and lets the user edit the title, and then either save or cancel, using two custom events to communicate back outwards.
Because of this we can easily reuse EditItem to create new Todos. Not only does this save us time, but it also insures that the user interface acts consistently.
Update the Header component to use EditItem like this:
# app/hyperstack/components/header.
class Header < HyperComponent
  before_mount { @new_todo = Todo.new }
  render(HEADER) do
    EditItem(todo: @new_todo)
    .on(:saved) { mutate @new_todo = Todo.new }
  end
end
What we have done is initialize an instance variable @new_todo to a new unsaved Todo item in the before_mount lifecycle method.
Then we pass the value @new_todo to EditItem, and when it is saved, we generate another new Todo and save it in the new_todo state variable.
When Header's state is mutated, it will cause a re-render of the Header, which will then pass the new value of @new_todo, to EditItem, causing that component to also re-render.
We don't care if the user cancels the edit, so we simply don't provide a :cancel event handler.
Once the code is added a new input box will appear at the top of the window, and when you type enter a new Todo will be added to the list.
However you will notice that the value of new Todo input box does not clear. This is subtle problem but it's easy to fix.
React treats the INPUT tag's defaultValue specially. It is only read when the INPUT is first mounted, so it does not react to changes like normal parameters. Our Header component does pass in new Todo records, but even though they are changing React does not update the INPUT.
React has a special param called key. React uses this to uniquely identify mounted components. It's used to keep track of lists of components, in this case it can also be used to indicate that the component needs to be remounted when the value of key is changed.
All objects in Hyperstack respond to the to_key method which will return a suitable unique key id, so all we have to do is pass todo as the key param, this will insure that as todo changes, we will re-initialize the INPUT tag.
...
INPUT(defaultValue: todo.title, key: todo) # add the special key param
...
Chapter 11: Adding Styling
We are just going to steal the style sheet from the benchmark Todo app, and add it to our assets.
Go grab the file in this repo here: https://github.com/hyperstack-org/hyperstack/blob/edge/docs/tutorial/assets/todo.css and copy it to a new file called todo.css in the app/assets/stylesheets/ directory.
You will have to refresh the page after changing the style sheet.
Now its a matter of updating the css classes which are passed to components via the class parameter.
Let's start with the App component. With styling it will look like this:
# app/hyperstack/components/app.rb
class App < HyperComponent
  include Hyperstack::Router
  render(SECTION, class: 'todo-app') do # add class todo-app
    Header()
    Route('/', exact: true) { Redirect('/all') }
    Route('/:scope', mounts: Index)
    Footer()
  end
end
The Footer component needs to have a UL added to hold the links nicely, and we can also use the NavLinks active_class param to highlight the link that is currently active:
# app/hyperstack/components/footer.rb
class Footer < HyperComponent
  include Hyperstack::Router::Helpers
  def link_item(path)
    # wrap the NavLink in a LI and
    # tell the NavLink to change the class to :selected when
    # the current (active) path equals the NavLink's path.
    LI { NavLink("/#{path}", active_class: :selected) { path.camelize } }
  end
  render(DIV, class: :footer) do   # add class footer
    UL(class: :filters) do         # wrap links in a UL element with class filters
      link_item(:all)
      link_item(:active)
      link_item(:completed)
    end
  end
end
For the Index component just add the main and todo-list classes.
# app/hyperstack/components/index.rb
class Index < HyperComponent
  include Hyperstack::Router::Helpers
  render(SECTION, class: :main) do         # add class main
    UL(class: 'todo-list') do              # add class todo-list
      Todo.send(match.params[:scope]).each do |todo|
        TodoItem(todo: todo)
      end
    end
  end
end
For the EditItem component we want the parent to pass any html parameters such as class along to the INPUT tag. We do this by adding the special other param that will collect any extra params, we then pass it along in to the INPUT tag. Hyperstack will take care of merging all the params together sensibly.
# app/hyperstack/components/edit_item.rb
class EditItem < HyperComponent
  param :todo
  fires :saved
  fires :cancel
  other :etc  # can be named anything you want
  after_mount { jQ[dom_node].focus }
  render do
    INPUT(etc, defaultValue: todo.title, key: todo)
    .on(:enter) do |evt|
      todo.update(title: evt.target.value)
      saved!
    end
    .on(:blur) { cancel! }
  end
end
Now we can add classes to the TodoItem's list-item, input, anchor tags, and to the EditItem component:
# app/hyperstack/components/todo_item.rb
class TodoItem < HyperComponent
  param :todo
  render(LI, class: 'todo-item') do # add the todo-item class
    if @editing
      EditItem(class: :edit, todo: todo)  # add the edit class
      .on(:saved, :cancel) { mutate @editing = false }
    else
      INPUT(type: :checkbox, class: :toggle, checked: todo.completed) # add the toggle class
      .on(:change) { todo.update(completed: !todo.completed) }
      LABEL { todo.title }
      .on(:double_click) { mutate @editing = true }
      A(class: :destroy) # add the destroy class and remove the -X- placeholder
      .on(:click) { todo.destroy }
    end
  end
end
In the Header we can send a different class to the EditItem component. While we are at it we will add the H1 { 'todos' } hero unit.
# app/hyperstack/components/header.
class Header < HyperComponent
  before_mount { @new_todo = Todo.new }
  render(HEADER, class: :header) do                   # add the 'header' class
    H1 { 'todos' }                                    # add the hero unit.
    EditItem(class: 'new-todo', todo: @new_todo)      # add 'new-todo' class
    .on(:saved) { mutate @new_todo = Todo.new }
  end
end
At this point your Todo App should be properly styled.
Chapter 12: Other Features
Show How Many Items Left In Footer
This is just a span that we add before the link tags list in the Footer component:
...
render(DIV, class: :footer) do
  SPAN(class: 'todo-count') do
    # pluralize returns the second param (item) properly
    # pluralized depending on the first param's value.
    "#{pluralize(Todo.active.count, 'item')} left"
  end
  UL(class: :filters) do
...
Add 'placeholder' Text To Edit Item
EditItem should display a meaningful placeholder hint if the title is blank:
...
INPUT(etc, placeholder: 'What is left to do today?',
            defaultValue: todo.title, key: todo)
.on(:enter) do |evt|
...
Don't Show the Footer If There are No Todos
In the App component add a guard so that we won't show the Footer if there are no Todos:
...
Footer() unless Todo.count.zero?
...
Congratulations! you have completed the tutorial.
Summary
You have built a small but feature rich full stack Todo application in less than 100 lines of code:
SLOC  
--------------
App:         9
Header:      8
Index:      10
TodoItem:   16
EditItem:   16
Footer:     16
Todo Model:  4
Rails Route: 4
--------------
Total:      83
The complete application is shown here:
# app/hyperstack/components/app.rb
class App < HyperComponent
  include Hyperstack::Router
  render(SECTION, class: 'todo-app') do
    Header()
    Route('/', exact: true) { Redirect('/all') }
    Route('/:scope', mounts: Index)
    Footer() unless Todo.count.zero?
  end
end
​
# app/hyperstack/components/header.
class Header < HyperComponent
  before_mount { @new_todo = Todo.new }
  render(HEADER, class: :header) do
    H1 { 'todos' }
    EditItem(class: 'new-todo', todo: @new_todo)
    .on(:saved) { mutate @new_todo = Todo.new }
  end
end
​
# app/hyperstack/components/index.rb
class Index < HyperComponent
  include Hyperstack::Router::Helpers
  render(SECTION, class: :main) do
    UL(class: 'todo-list') do
      Todo.send(match.params[:scope]).each do |todo|
        TodoItem(todo: todo)
      end
    end
  end
end
​
# app/hyperstack/components/footer.rb
class Footer < HyperComponent
  include Hyperstack::Router::Helpers
  def link_item(path)
    LI { NavLink("/#{path}", active_class: :selected) { path.camelize } }
  end
  render(DIV, class: :footer) do
    SPAN(class: 'todo-count') { "#{pluralize(Todo.active.count, 'item')} left" }
    UL(class: :filters) do
      link_item(:all)
      link_item(:active)
      link_item(:completed)
    end
  end
end
​
# app/hyperstack/components/todo_item.rb
class TodoItem < HyperComponent