opal-rails is available to make opal work directly inside rails applications.
If you wish to build a standalone application, you can use a simple rake task to help. Opal uses a set of load paths internally to resolve code dependencies, so it is always a good idea to keep your ruby code inside a directory.
Start by making a app/application.rb file to hold our demo code:
# app/application.rb require "opal" puts "Wow, running in Opal!"
You will notice the require "opal" line which will automatically include the opal runtime and corelib into our output, giving us access to the puts() method.
To build this, we need a rake task to load a new opal environment, add our app/ directory to the load path, and then to build our target file application.rb which will be found because it is inside our added load path.
# Rakefile desc "Build our app to build.js" task :build do env = Opal::Environment.new env.append_path "app" File.open("build.js", "w+") do |out| out << env["application"].to_s end end
Now, if you run rake build you will get the build.js output file with our application compiled, with the opal runtime included as well.
To run the application, lets create a very simple html file:
<!DOCTYPE html> <html> <head> <script src="build.js"></script> </head> <body> </body> </html>
Now, open this html file and check the browsers console. You should see our message printed in the console.
