Opal Rails

Rails bindings for Opal. (Changelog)

If you want to integrate Opal via Webpack please refer to opal-webpack-loader installation instructions.

ℹ️ Webpack and ES6 modules are not yet officially supported, but we're working on it thanks to the awesome work done in opal-webpack-loader.

In your Gemfile

gem 'opal-rails'

Run opal:install Rails generator to add app/assets/javascript to your asset-pipeline manifest in app/assets/config/manifest.js:

bin/rails g opal:install

The following automatically gets added to your configuration for the compiler when running the opal:install Rails generator:

config/initializers/opal.rb

# Compiler options
Rails.application.configure do
  config.opal.method_missing_enabled   = true
  config.opal.const_missing_enabled    = true
  config.opal.arity_check_enabled      = true
  config.opal.freezing_stubs_enabled   = true
  config.opal.dynamic_require_severity = :ignore
end

Check out the full list of the available configuration options at: lib/opal/config.rb.

You may optionally add configuration for rendering assigns when using the template handler from actions:

config/initializers/opal.rb

Rails.application.configure do
  # ...
  config.opal.assigns_in_templates = true
  config.opal.assigns_in_templates = :locals # only locals
  config.opal.assigns_in_templates = :ivars # only instance variables
end

Local and instance variables will be sent down to the view after converting their values to JSON.

This example assumes Rails 7 and having followed the Installation instructions.

1- Delete app/javascript/application.js

2- Enable the following lines in the generated app/assets/javascript/application.js.rb below require "opal":

puts "hello world!"
require "native"
$$[:document].addEventListener :DOMContentLoaded do
  $$[:document][:body][:innerHTML] = '<h2>Hello World!</h2>'
end

3- Run rails g scaffold welcome

4- Run rails db:migrate

5- Clear app/views/welcomes/index.html.erb (empty its content)

6- Run rails s

7- Visit http://localhost:3000/welcomes

In the browser webpage, you should see:

Also, you should see hello world! in the browser console.

This example assumes Rails 5.

1. Rename app/assets/javascripts/application.js to app/assets/javascripts/application.js.rb
2. Replace the Sprockets directives with plain requires

# Require the opal runtime and core library
require 'opal'

# For Rails 5.1 and above, otherwise use 'opal_ujs'
require 'rails_ujs'

# Require of JS libraries will be forwarded to sprockets as is
require 'turbolinks'

# a Ruby equivalent of the require_tree Sprockets directive is available
require_tree '.'

puts "hello world!"

require 'opal'
require 'opal_ujs'
require 'turbolinks'
require_tree '.' # a Ruby equivalent of the require_tree Sprockets directive is available

# ---- YOUR FANCY RUBY CODE HERE ----
#
# Examples:

# == Print something in the browser's console
puts "Hello world!"
pp hello: :world
require 'console'
$console.log %w[Hello world!]

# == Use Native to wrap native JS objects, $$ is preconfigured to wrap `window`
require 'native'
$$.alert "Hello world!"

# == Do some DOM manipulation with jQuery
require 'opal-jquery'
Document.ready? do
  Element.find('body').html = '<h1>Hello world!</h1>'
end

# == Or access the DOM api directly
$$[:document].addEventListener(:DOMContentLoaded, -> {
  $$[:document].querySelector('body')[:innerHTML] = '<h1>Hello world!</h1>'
})

If you want to use application.js (instead of application.js.rb) and keep using Sprockets directives, you'll need to load the Opal files you require via Sprockets manually, e.g.:

//= require opal
//= require rails_ujs
//= require turbolinks
//= require_tree .
//= require app

Opal.require('opal');
Opal.require('app');

You can use it for your views too:

# app/controllers/posts_controller.rb

def create
  @post = Post.create!(params[:post])
  render type: :js, locals: {comments_html: render_to_string(@post.comments)}
end

Assigned instance that would normally be available in your views are converted to JSON objects first.

# app/views/posts/create.js.opal

post = Element.find('.post')
post.find('.title').html    = @post[:title]
post.find('.body').html     = @post[:body]
post.find('.comments').html = comments_html

By default opal-rails, will NOT forward any instance and local variable you'll pass to the template.

This behavior can be enabled by setting Rails.application.config.opal.assigns_in_templates to true in config/initializers/assets.rb:

Rails.application.configure do
  # ...
  config.opal.assigns_in_templates = true
  # ...
end

Of course you need to require haml-rails separately since its presence is not assumed

-# app/views/posts/show.html.haml

%article.post
  %h1.title= post.title
  .body= post.body

%a#show-comments Display Comments!

.comments(style="display:none;")
  - post.comments.each do |comment|
    .comment= comment.body

:opal
  Document.ready? do
    Element.find('#show-comments').on :click do |click|
      click.prevent_default
      click.current_target.hide
      Element.find('.comments').effect(:fade_in)
    end
  end

Extracted to (unreleased) opal-rspec-rails

Add this line to your Gemfile:

gem 'opal-rspec-rails', github: 'opal/opal-rspec-rails'

Upcoming as opal-minitest-rails

As long as the templates are inside the Sprockets/Opal load path, then you should be able to just require them.

Let's say we have this template app/views/shared/test.haml:

.row
  .col-sm-12
    = @bar

We need to make sure Opal can see and compile that template. So we need to add the path to sprockets:

# config/initializers/opal.rb
Rails.application.config.assets.paths << Rails.root.join('app', 'views', 'shared').to_s

Now, somewhere in application.rb you need to require that template, and you can just run it through Template:

# app/assets/javascripts/application.rb
require 'opal'
require 'opal-haml'
require 'test'

@bar = "hello world"

template = Template['test']
template.render(self)
# =>  '<div class="row"><div class="col-sm-12">hello world</div></div>'

Just use Opal.use_gem in your asset initializer (config/initializers/assets.rb).

Example:

Opal.use_gem 'cannonbol'

Run the specs:

bin/setup
bin/rake

Inspect the test app:

bin/rackup
# visit localhost:9292

Tinker with a sandbox app:

bin/sandbox # will re-create the app
bin/rails s # will start the sandbox app server
# visit localhost:3000

© 2012-2022 Elia Schito

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