# Opal & Sprockets
Opal comes with built-in sprockets support, and provides a simple `Opal::Server`
class to make it easy to get a rack server up and running for trying out opal.
This server will automatically recompile ruby sources when they change, meaning
you just need to refresh your page to autorun.
## Getting setup
Add `opal` to a `Gemfile`:
```ruby
#Gemfile
source 'https://rubygems.org'
gem 'opal', '>= 0.6.0'
```
And install with `bundle install`.
We need a directory to hold our opal code, so create `app/` and add a simple
demo script to `app/application.rb`:
```ruby
# app/application.rb
require 'opal'
puts "hello world"
```
Finally, we need a html page to run, so create `index.html`:
```html
opal server example
```
## Using Opal::Server
`Opal::Server` can be run like any rack app, so just add a `config.ru` file:
```ruby
# config.ru
require 'bundler'
Bundler.require
run Opal::Server.new { |s|
s.append_path 'app'
s.main = 'application'
s.index_path = 'index.html'
}
```
This rack app simply adds our `app/` directory to opal load path, and sets our
main file to `application`, which will be found inside `app/`.
## Running the app
Run `bundle exec rackup` and visit the page `http://localhost:9292` in any
browser. Observe the console to see the printed statement.
You can just change `app/application.rb` and refresh the page to see any changes.