rails server error on ubuntu - ruby-on-rails

Question

I am following ruby on rails getting started guide ( http://guides.rubyonrails.org/getting_started.html )
I installed ruby and rails as it is suggested in the guide but when I try to execute:
bin/rails server
I see the following error in the terminal:
Warning: Running `gem pristine --all` to regenerate your installed gemspecs (and deleting then reinstalling your bundle if you use bundle --path) will improve the startup performance of Spring.
/var/lib/gems/2.1.0/gems/bundler-1.11.2/lib/bundler/runtime.rb:80:in `rescue in block (2 levels) in require': There was an error while trying to load the gem 'uglifier'. (Bundler::GemRequireError)
from /var/lib/gems/2.1.0/gems/bundler-1.11.2/lib/bundler/runtime.rb:76:in `block (2 levels) in require'
from /var/lib/gems/2.1.0/gems/bundler-1.11.2/lib/bundler/runtime.rb:72:in `each'
from /var/lib/gems/2.1.0/gems/bundler-1.11.2/lib/bundler/runtime.rb:72:in `block in require'
from /var/lib/gems/2.1.0/gems/bundler-1.11.2/lib/bundler/runtime.rb:61:in `each'
from /var/lib/gems/2.1.0/gems/bundler-1.11.2/lib/bundler/runtime.rb:61:in `require'
from /var/lib/gems/2.1.0/gems/bundler-1.11.2/lib/bundler.rb:99:in `require'
from /home/soroosh/rails/blog/config/application.rb:7:in `<top (required)>'
from /var/lib/gems/2.1.0/gems/railties-4.2.5.1/lib/rails/commands/commands_tasks.rb:78:in `require'
from /var/lib/gems/2.1.0/gems/railties-4.2.5.1/lib/rails/commands/commands_tasks.rb:78:in `block in server'
from /var/lib/gems/2.1.0/gems/railties-4.2.5.1/lib/rails/commands/commands_tasks.rb:75:in `tap'
from /var/lib/gems/2.1.0/gems/railties-4.2.5.1/lib/rails/commands/commands_tasks.rb:75:in `server'
from /var/lib/gems/2.1.0/gems/railties-4.2.5.1/lib/rails/commands/commands_tasks.rb:39:in `run_command!'
from /var/lib/gems/2.1.0/gems/railties-4.2.5.1/lib/rails/commands.rb:17:in `<top (required)>'
from /home/soroosh/rails/blog/bin/rails:9:in `require'
from /home/soroosh/rails/blog/bin/rails:9:in `<top (required)>'
from /var/lib/gems/2.1.0/gems/spring-1.6.3/lib/spring/client/rails.rb:28:in `load'
from /var/lib/gems/2.1.0/gems/spring-1.6.3/lib/spring/client/rails.rb:28:in `call'
from /var/lib/gems/2.1.0/gems/spring-1.6.3/lib/spring/client/command.rb:7:in `call'
from /var/lib/gems/2.1.0/gems/spring-1.6.3/lib/spring/client.rb:28:in `run'
from /var/lib/gems/2.1.0/gems/spring-1.6.3/bin/spring:49:in `<top (required)>'
from /var/lib/gems/2.1.0/gems/spring-1.6.3/lib/spring/binstub.rb:11:in `load'
from /var/lib/gems/2.1.0/gems/spring-1.6.3/lib/spring/binstub.rb:11:in `<top (required)>'
from /usr/lib/ruby/2.1.0/rubygems/core_ext/kernel_require.rb:55:in `require'
from /usr/lib/ruby/2.1.0/rubygems/core_ext/kernel_require.rb:55:in `require'
from /home/soroosh/rails/blog/bin/spring:13:in `<top (required)>'
from bin/rails:3:in `load'
from bin/rails:3:in `<main>'
I am using ubuntu 15.10 , ruby 2.1 and rails4.2.5.1

Answer 1

If you look closely at the error message, this is the important line:
There was an error while trying to load the gem 'uglifier'.
Uglifier is a Javascript wrapper, so it will need a Javascript interpreter. I recommend installing NodeJS:
sudo apt-get install nodejs
read more about uglifier: https://github.com/lautis/uglifier