What is Sinatra?
Let’s get a taste for Sinatra by building a simple application that displays a random joke on each page visit or refresh. Here’s the link to source code.
Create project directory:
mkdir sinatra-demo-app && cd sinatra-demo-app
Initialize Git repo:
source 'https://rubygems.org' gem "sinatra", "~> 2.0" gem "rerun", "~> 0.13.0" gem "httparty", "~> 0.18.1"
sinatra– the gem that contains the actual Sinatra web framework.
rerun– used in order to restart Sinatra whenever we make any code changes.
httparty– lightweight Ruby HTTP client that we’ll use later.
Create first route
Create a minimal
app.rb in your project root.
require 'sinatra' get '/' do 'Hello world' end
Inside a terminal, run:
rerun 'ruby app.rb'
Visit http://localhost:4567 and you should see ‘Hello world’.
Thanks to the
rerun gem, any changes you make to
app.rb should restart Sinatra and apply your changes. Feel free to change ‘Hello world’ to something else to see your changes reflected.
Render ERB template
Sinatra makes it a breeze to render dynamic ERB templates. Change
app.rb to the following:
require 'sinatra' get '/' do erb :home end
This will render a
views/home.erb file. You can also make use of layouts and partials for more advanced use cases (see docs for more info).
Visit http://localhost:4567 and you should see an HTML page with ‘Hello world’ rendered inside a
Passing data to views
Let’s spice things up a little bit by integrating an open-source Joke API (seems to be down at the moment) and display a random joke on the page.
We’ll use the
httparty gem we added earlier in order to call this API.
require 'sinatra' require 'httparty' get '/' do @joke = HTTParty.get('https://official-joke-api.appspot.com/random_joke') erb :home end
Sinatra will render the
views/home.erb template within the same context as the route handler which means you can access the
@joke instance variable inside our template.
<h3><%= @joke['setup'] %></h3> <h2><%= @joke['punchline'] %></h2>
Visit http://localhost:4567 and you should see a random joke each time.