Question

I new in rails , so I have silly question
while starting rails server I’ve got this mistake

rails s
/var/lib/gems/1.8/gems/execjs-1.4.0/lib/execjs/runtimes.rb:51:in `autodetect': Could not find a JavaScript runtime. See https://github.com/sstephenson/execjs for a list of available runtimes. (ExecJS::RuntimeUnavailable)
    from /var/lib/gems/1.8/gems/execjs-1.4.0/lib/execjs.rb:5
    from /var/lib/gems/1.8/gems/coffee-script-2.2.0/lib/coffee_script.rb:1:in `require'
    from /var/lib/gems/1.8/gems/coffee-script-2.2.0/lib/coffee_script.rb:1
    from /var/lib/gems/1.8/gems/coffee-script-2.2.0/lib/coffee-script.rb:1:in `require'
    from /var/lib/gems/1.8/gems/coffee-script-2.2.0/lib/coffee-script.rb:1
    from /var/lib/gems/1.8/gems/coffee-rails-3.2.2/lib/coffee-rails.rb:1:in `require'
    from /var/lib/gems/1.8/gems/coffee-rails-3.2.2/lib/coffee-rails.rb:1
    from /var/lib/gems/1.8/gems/bundler-1.2.3/lib/bundler/runtime.rb:68:in `require'
    from /var/lib/gems/1.8/gems/bundler-1.2.3/lib/bundler/runtime.rb:68:in `require'
    from /var/lib/gems/1.8/gems/bundler-1.2.3/lib/bundler/runtime.rb:66:in `each'
    from /var/lib/gems/1.8/gems/bundler-1.2.3/lib/bundler/runtime.rb:66:in `require'
    from /var/lib/gems/1.8/gems/bundler-1.2.3/lib/bundler/runtime.rb:55:in `each'
    from /var/lib/gems/1.8/gems/bundler-1.2.3/lib/bundler/runtime.rb:55:in `require'
    from /var/lib/gems/1.8/gems/bundler-1.2.3/lib/bundler.rb:128:in `require'
    from /home/gorysko/rails/rails_project/first_app/config/application.rb:7
    from /var/lib/gems/1.8/gems/railties-3.2.9/lib/rails/commands.rb:53:in `require'
    from /var/lib/gems/1.8/gems/railties-3.2.9/lib/rails/commands.rb:53
    from /var/lib/gems/1.8/gems/railties-3.2.9/lib/rails/commands.rb:50:in `tap'
    from /var/lib/gems/1.8/gems/railties-3.2.9/lib/rails/commands.rb:50
    from script/rails:6:in `require'
    from script/rails:6

But all installation was made as in book written and all dependencies are good too

Answer 1

Try adding this line to your gemfile

gem 'therubyracer'

It lets you evaluate JavaScript from within Ruby. You can check it out here.