1. Debugging Rails 3 Applications
Nathan Broadbent
Onboard Coding Ltd.
https://twitter.com/ndbroadbent
http://github.com/ndbroadbent

2. Topics
● Debugging Ruby
– debugger, awesome_print, pry
● Debugging Rails errors
– better_errors, Errbit
● Debugging JavaScript with Chrome
– Chrome Console, breakpoints, AJAX errors
● Debugging with Git
– git blame, git bisect

3. Debugging Ruby

4. debugger
● Use 'debugger' gem for Ruby 1.9.2 and 1.9.3
● commands
– next
– step
– list
– continue
– break

5. awesome_print
● Ruby library that pretty prints Ruby objects in
full color, exposing their internal structure with
proper indentation.

6. Pry Overview
● Powerful alternative to IRB / debugger
● Source code / documentation browsing
● Syntax highlighting
● Configure via ~/.pryrc

7. Configure Pry
● simple ~/.pryrc
– show Rails/Ruby version in prompt
– add awesome_print gem

8. Use Pry with Rails
● gem 'pry-rails'
● gem 'pry-debugger'
– Adds step, next, continue, ... commands
● gem 'pry-doc'
– Adds docs for Ruby

9. Pry Commands
● show-method
● show-doc
– show-doc Array#join
● ls
● cd
– cd Array; show-doc join

10. Pry Shell Integration
● Open file in editor, run rake task, etc.
● edit
– prepare a block code from your editor. When file is
closed, it will be executed
● edit-method
– Jump to a place in your project, handy for opening
files from gems

11. Learn more about Pry at
http://pryrepl.org/

12. Debugging
Rails

13. better_errors

14. better_errors
● Replaces the standard Rails error page with a
much better and more useful error page
● Source code inspection for all stack frames
(with syntax highlighting)
● Local and instance variable inspection
● Live REPL on every stack frame
– REPL = read, eval, print, loop

15. Errbit
open source, self-hosted error catcher

16. Errbit
open source, self-hosted error catcher
● Open source alternative to Airbrake service
● Catches Ruby and JavaScript errors
● Notify on 1st, 10th, 50th, 100th error
– Email, SMS, Campfire, IRC
● Issue tracker integration
– GitHub, Pivotal, Redmine, Gitlab, etc.
● Source code integration
GitHub, Bitbucket, Gitlab etc.

17. Debugging
JavaScript
with Chrome

18. Chrome Console Overview
● Breakpoints
– Set manually, or with a debugger statement
– Pause on All/Uncaught Exceptions
– Break on events
● DOM Mutation
● XHR
● Event Listeners
● console.log()
– console.log('multiple', params, 'allowed')
● console.trace()

19. Debugging with

20. git blame
● Find out which commit changed this line
● Helps to understand the reasoning behind the
change

21. git bisect
●
Binary search for commit history
●
Find out exactly when a test started failing, or when an error
started to occur
git bisect start
git bisect good e401315
git bisect bad master
git bisect run rspec spec/models/book_spec.rb
... wait a bit ...
5243cafebabe is the last bad commit

22. Questions or
Comments?