Rack::Component

Like a React.js component, a Rack::Component implements a render method that takes input data and returns what to display.

You can combine Components to build complex features out of simple, easily testable units.

Installation

Add this line to your application's Gemfile:

gem 'rack-component', require: 'rack/component'

And then execute:

$ bundle

Or install it yourself as:

$ gem install rack-component

API Reference

Please see the YARD docs on rubydoc.info

Usage

Subclass Rack::Component and #call it:

require 'rack/component'
class Useless < Rack::Component
end

Useless.call #=> the output Useless.new.render

The default implementation of #render is to yield the component instance to whatever block you pass to Component.call, like this:

Useless.call { |instance| "Hello from #{instance}" }
#=> "Hello from #<Useless:0x00007fcaba87d138>"

Useless.call do |instance|
  Useless.call do |second_instance|
    "      <h1>Hello from \#{instance}</h1>\n      <p>And also from \#{second_instance}\"</p>\n    HTML\n  end\nend\n# =>\n# <h1>Hello from #<Useless:0x00007fcaba87d138></h1>\n# <p>And also from #<Useless:0x00007f8482802498></p>\n"

Implement #render or add instance methods to make Components do work

Peruse the specs for examples of component chains that handle data fetching, views, and error handling in Sinatra and raw Rack.

Here's a component chain that prints headlines from Daring Fireball’s JSON feed:

require 'rack/component'

# Make a network request and return the response
class Fetcher < Rack::Component
  require 'net/http'
  def initialize(uri:)
    @response = Net::HTTP.get(URI(uri))
  end

  def render
    yield @response
  end
end

# Parse items from a JSON Feed document
class JSONFeedParser < Rack::Component
  require 'json'
  def initialize(data)
    @items = JSON.parse(data).fetch('items')
  end

  def render
    yield @items
  end
end

# Render an HTML list of posts
class PostsList < Rack::Component
  def initialize(posts:, style: '')
    @posts = posts
    @style = style
  end

  def render
    "      <ul style=\"\#{@style}\">\n        \#{@posts.map(&ListItem).join}\"\n      </ul>\n    HTML\n  end\n\n  ListItem = ->(post) { \"<li>\#{post['title']}</li>\" }\nend\n\n# Fetch JSON Feed data from daring fireball, parse it, render a list\nFetcher.call(uri: 'https://daringfireball.net/feeds/json') do |data|\n  JSONFeedParser.call(data) do |items|\n    PostsList.call(posts: items, style: 'background-color: red')\n  end\nend\nend\n#=> A <ul> full of headlines from Daring Fireball\n\n"

Development

After checking out the repo, run bin/setup to install dependencies. Then, run rake spec to run the tests. You can also run bin/console for an interactive prompt that will allow you to experiment.

To install this gem onto your local machine, run bundle exec rake install. To release a new version, update the version number in version.rb, and then run bundle exec rake release, which will create a git tag for the version, push git commits and tags, and push the .gem file to rubygems.org.

Contributing

Bug reports and pull requests are welcome on GitHub at https://github.com/chrisfrank/rack-component.

License

MIT