This document summarizes various debugging techniques for Ruby on Rails applications. It discusses using the debugger, awesome_print and Pry gems to debug Ruby code. It also covers using the better_errors and Errbit gems to debug Rails errors and exceptions. The document provides an overview of debugging JavaScript using the Chrome developer tools console. It also discusses using git blame and git bisect to help debug code changes that may have introduced bugs.

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?