As most WordPress users know, plugins can be used to enhance WordPress sites in many ways. Unfortunately, they can also easily break your work. From javascript errors to buggy updates, from slow-performing code to stylesheet conflicts, this talk aims to help users identify and troubleshoot problems with plugins as they work on their creations.

1. @ylefebvre
ylefebvre.ca
Plugins
A Double-Edged Sword
Yannick Lefebvre
Plugin Developer
Presentation available at:
yannickcorner.nayanna.biz/wcmtl2013

2. @ylefebvre
ylefebvre.ca
Plugins: A Double-Edged Sword
● About me
● The power of plugins
● The wild nature of plugins
● Site-building strategies
● Troubleshooting plugin issues
● Handling problematic updates
● Avoiding bad plugin breakups
● Conclusions

3. @ylefebvre
ylefebvre.ca
About ME
● Using WordPress since 2004
● Released first plugin (Link Library) in 2005
● Released 8 Plugins on the official repository

4. @ylefebvre
ylefebvre.ca
The Power of Plugins
● Custom code modules that can be
downloaded and added to WordPress
● Can change almost any aspect of
WordPress
– Add extra content / new functionality
– Modify / enhance default behavior
– Simplify complex tasks

5. @ylefebvre
ylefebvre.ca
The Power of Plugins
● Allow integrators to create custom content
without modifying core
● Large developer community
● More than 25 000 plugins available, plus
premium plugins!

6. @ylefebvre
ylefebvre.ca
The Wild Nature of Plugins
● Only available on self-hosted installs
● No enforced coding standard
● Difficult to assess performance and quality
● No code reviews
● No easy way to identify bad updates
● Difficult to predict interaction with site and
other plugins

7. @ylefebvre
ylefebvre.ca
Building a site with plugins...
...can feel A BIT UNSTABLE

8. @ylefebvre
ylefebvre.ca
Site-building strategies
● Perform due diligence on a
plugin
– Version compatibility
– Number of downloads
– Positive / Negative ratings
– Number of resolved support
threads

9. @ylefebvre
ylefebvre.ca
Site-building strategies
● Assess plugin functionality through docs
and examples
● Create a development site to test before
deployment
● Only add one plugin at a time

10. @ylefebvre
ylefebvre.ca
Site-building strategies
● Measure site performance before and after
plugin installation
– Front-end and admin pages
– Log out to see regular visitors performance

11. @ylefebvre
ylefebvre.ca
Troubleshooting plugin issues
● Deactivate the last plugin installed
● Deactivate all other plugins and bring back
one at a time to identify source of conflict
● Visit the official plugin page
– Installation procedure
– FAQ
– Support Forum
● Contact the plugin author

12. @ylefebvre
ylefebvre.ca
TROUBLESHOOTING Styling issues
● Many plugins render content on site pages
● Usually provide their own styling for this
content
● Stylesheets don't always like to agree with
each other

13. @ylefebvre
ylefebvre.ca
TROUBLESHOOTING Styling issues

14. @ylefebvre
ylefebvre.ca
TROUBLESHOOTING Styling issues
● Theme can be modified
– Users don't always know full impact of changes
● Plugin stylesheet can be modified
– Avoid changing plugin files (Plugin updates
override file changes)
– Backup files if no other option
– Some plugins have stylesheet editors
– The !important CSS keyword is very useful

15. @ylefebvre
ylefebvre.ca
Troubleshooting jQuery issues
● Most animated / dynamic site elements
today are powered by jQuery
● jQuery conflicts can easily occur when a
theme and one or more plugins are mixed
● A conflict usually breaks all jQuery elements
on a site

16. @ylefebvre
ylefebvre.ca
● FireBug (getfirebug.com) is the perfect tool
to identify jQuery / javascript conflicts
Troubleshooting jQuery issues

17. @ylefebvre
ylefebvre.ca
TYPICAL JQUERY ISSUES
● More than one copy of jQuery.js is loaded
– Verify in page source code
– Each additional copy wipes out previous work
● An incompatible version of jQuery is loaded
– E.g. Google API version loaded for speed boost

18. @ylefebvre
ylefebvre.ca
TYPICAL JQUERY ISSUES
● Multiple versions of javascript/jQuery
library are loaded by different plugins
● Theme or plugin jQuery code uses
unavailable jQuery shorthand
– All jQuery calls should use jQuery long-form
instead of $ or re-create the shorthand
themselves

19. @ylefebvre
ylefebvre.ca
Troubleshooting jQuery issues
● In the previous example, two plugins were
loading different versions of the same
jQuery library

20. @ylefebvre
ylefebvre.ca
Troubleshooting upload issues
● Lack of permissions
– Increase write permissions on upload folder
● Exceeding server maximum upload file size
– Not controlled by WordPress
– Set in server php.ini file (default often 8 MB)
– Plugins can display current settings (e.g.
WordPress phpinfo)
– See with hosting company to change settings

21. @ylefebvre
ylefebvre.ca
Troubleshooting upload issues

22. @ylefebvre
ylefebvre.ca
Handling problematic updates
● After updating a plugin
– Your entire site stopped working
– All of your javascript-based code stopped
working
– The plugin's expected output no longer works

23. @ylefebvre
ylefebvre.ca

24. @ylefebvre
ylefebvre.ca
● Deactivate and reactivate updated plugin(s)
– Ensures that activation routines are executed
(e.g. Database updates, creation of new option
default values)
– Essential when uploading plugins via FTP
– Plugin reboot
Handling problematic updates

25. @ylefebvre
ylefebvre.ca
Handling problematic updates
● Identify the problematic plugin through
error messages (often contain plugin path)
● Revert to the plugin's previous version from
your most recent site backup

26. @ylefebvre
ylefebvre.ca
Handling problematic updates
● Check for previous versions

27. @ylefebvre
ylefebvre.ca
Handling problematic updates
● Not all plugins list previous versions

28. @ylefebvre
ylefebvre.ca
FIND previous PLUGIN versions
● Trac is a web-based interface for the
Subversion system where all WordPress.org
plugins are stored

29. @ylefebvre
ylefebvre.ca
FIND previous PLUGIN versions
Current plugin version is usually trunk

30. @ylefebvre
ylefebvre.ca
FIND previous PLUGIN versions
Viewing the plugin trunk and
selecting the Revision Log

31. @ylefebvre
ylefebvre.ca
FIND previous PLUGIN versions
Select latest version in left column and known
working version in right column

32. @ylefebvre
ylefebvre.ca
FIND previous PLUGIN versions
Click View changes

33. @ylefebvre
ylefebvre.ca
FIND previous PLUGIN versions

34. @ylefebvre
ylefebvre.ca
FIND previous PLUGIN versions
At page bottom, download archive containing
old versions of changed files

35. @ylefebvre
ylefebvre.ca
FIND previous PLUGIN versions
● Once you have the previous version
– Upload to your server via FTP
– Stop updating until you see a message
indicating that the issue has been resolved

36. @ylefebvre
ylefebvre.ca
Avoiding bad plugin breakups
● User-triggered breakup
– Better solution available
– Extra functionality no longer required
● Plugin-triggered breakup
– Plugin converted to paid model
– End of development life
– Lack of support for new versions

37. @ylefebvre
ylefebvre.ca
Avoiding bad plugin breakups
● Many plugins store user information to the
database to provide additional capabilities
– Custom fields
– Custom post types
– Custom tables
● Not all developers consider what will happen
if users decide to stop using their plugin

38. @ylefebvre
ylefebvre.ca
Avoiding bad plugin breakups
● Before deploying plugins, analyze the
effects of deactivation to prepare for
eventual breakup
– Clean removal
– Ease or difficulty of accessing custom data
– Core data modifications
– Broken site

39. @ylefebvre
ylefebvre.ca
Conclusions
● Plugins are amazing tools that can greatly
enhance your site
● Plugins are potential liabilities that can break
your site
● When used with caution, plugins bring
limitless possibilities to web site creation

40. @ylefebvre
ylefebvre.caBryanBerg,Architect

41. @ylefebvre
ylefebvre.ca
Recommended Readings
● Learn about plugin development
– WordPress Plugin Development
Cookbook by Yannick Lefebvre,
published by Packt Publishing
(packtpub.com)
– Use code WCMONTREAL13 to get 75%
off ebook on packtpub.com (until Aug 1)
● Find help when you run into issues
– WordPress Support Forum
(wordpress.org/support)
● Today's presentation available at:
– http://yannickcorner.nayanna.biz/wcmtl2013

42. @ylefebvre
ylefebvre.ca
Thank you for attending this talk
on Plugins
Questions?
Presentation: http://yannickcorner.nayanna.biz/wcmtl2013
ylefebvre@gmail.com
profiles.wordpress.org/users/jackdewey
Use code
WCMONTREAL13
to get 75 off%
WordPress Plugin
Development
Cookbook ebook
on packtpub.com
(until Aug 1)