This is a new and improved version of my talk Understanding WordPress Filters & Actions. Based on the feedback I got from that talk I simplified my presentation and included more granular explanations. The goal of this presentation is to help folks understand a little better what goes on behind the scenes of their favorite themes and plugins, and help them get started coding their own if they so desire. Enjoy!

1. build create W O R D C A M P G R A N D R A P I D S
W O R D P R E S S H O O K S
I N T R O D U C T I O N T O
build create W O R D C A M P G R A N D R A P I D S

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H I .
Designer, developer,
marketer, shit-talker, etc.
Co-owner build/create studios
@buildcreate
@wilsonography
buildcreate.com
I ’ M I A N , N I C E T O M E E T Y O U .

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M Y S E L F I S H G O A L S F O R Y O U
I want you to walk away from this feeling a little less
hacky, a little more informed, and most of all inspired.
I want you to have an “Ah ha!” moment, where suddenly
your understanding of WordPress becomes that much
clearer, and you can’t wait to get out of this room to try
out your new knowledge.
Here goes nothing…

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L E T ’ S TA L K A B O U T H O O K S
“Hooks enable us to literally hook into parts of the
WordPress page lifecycle to retrieve, insert, or modify
data, or they allow us to take certain actions behind the
scenes.”
- T O M M C FA R L I N @ T U T S P L U S

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A W O R L D W I T H O U T H O O K S

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I T ’ S P R E T T Y D A M N H A C K Y
• Including extra PHP files for ajax
requests
• Hacking into plugins to change
display/functionality
• Hacking *gasp* WP core files
• Hacking theme files (when you
should be using a child theme)
• Hackity hack hack hack.

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F I LT E R S
• Applying changes to
content/data
• Uses functions:
• apply_filters()
This is the hook.
• add_filter()
This is what you use to tie into
the hook.
A C T I O N S
• Hooks your functions into
an action in WP
• Uses functions:
• do_action()
This is the hook.
• add_action()
This is what you use to tie into
the hook.

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Filters and Actions are nearly the same thing in WordPress,
almost identical syntax, capabilities, and limitations.
The difference is how you use them.

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F I LT E R S
• Change something you’re
pulling out of WP- the
content, a media file, etc.
• Change something you’re
putting into the WP database
A C T I O N S
• Tying into existing WP processes,
like sending email, saving a post,
saving a comment, etc.
• Add an action to your plugin/
theme to allow other developers
to manipulate it without hacking
W H E N S H O U L D W E U S E T H E S E
L O V E LY H O O K S ?

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A K A A L L T H E D A M N
T I M E . I T ’ S M A G I C .

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S O , L E T S M A K E S O M E M A G I C …

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A N AT O M Y O F A H O O K
add_filter( $hook, $function_to_add, $priority, $accepted_args );
The name of the
filter to hook into
Your function you
want to run when
the filter is applied
Lower numbers =
earlier execution
of your filter
Any additional
arguments you
want to pass to
the function
add_action( $hook, $function_to_add, $priority, $accepted_args );

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S O M E N I T T Y G R I T T Y N O T E S
• Usually a filter comes with one argument by default- the content that you’re going to be
modifying. Some filters accept additional arguments as specified in the matching
“apply_filter” call. Make sure you’re aware of these when you use the filter.
• Though you can pass all kinds of arguments into your filter function, the only thing you
get back is the value of what you’re filtering. So for example if you’re using
‘the_content’ filter, and you have your function accept the post ID as well as the default
content argument, all you can safely return at the end of your function is the content.
• Actions don’t return any data, only true. Always true. Deal with it.
• Actions also allow you to pass “all” as the hook name to tie into every hook. Yikes.
• You can pass a class method like so: array( 'My_Class', ‘my_class_method’ ).
This is especially useful in plugin development when ofttimes your plugin has several
class methods.

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U P N E X T: A S U P E R D U P E R S I M P L E E X A M P L E

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add_filter(‘the_content’, ‘my_filter_function’, 10);
function my_filter_function($content) {
$output = '<div>'.$content.'</div>';
return $output;
}

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add_filter(‘the_content’, ‘my_filter_function’, 10);
function my_filter_function($content) {
$output = '<div>'.$content.'</div>';
return $output;
}
This variable comes
through from the
matching apply_filter()
The name of the
filter to hook into
Your function you want to
run when the filter is applied
Lower numbers = earlier
execution of your filter

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D E F I N I N G Y O U R H O O K S
apply_filter( $tag, $value, $arg );
The name of the
filter to hook into
The value you
want to modify
with the filter
One or more additional arguments
passed to the filter function
do_action( $tag, $arg);
See? The only difference is that we aren’t
passing a value to modify.

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E X A M P L E H O O K S
• save_post - Action: runs whenever a post or page is created/updated. Useful for saving custom
meta information.
• add_meta_boxes - Action: used to add meta boxes to the WordPress edit screen. You’d then
probably wind up using the save_post action to validate the data before saving.
• wp_enqueue_scripts - Action: used to add styles and scripts to the front end. Used a lot in themes
and plugins. There’s also an admin and login version for adding styles and scripts to those areas.
• the_content, the_title, etc - Filter: used to modify the content and title respectively. There are also
filters to modify these in the editor on the backend of WordPress.
• wp_authenticate_user - Filter: used to tie into the authentication process and run your own
authentication function on the user’s login form submission.
• body_class - Filter: say you want to add some classes to the body based on various conditions
(assuming you’re using the body_class function in your template), you would use this hook in your
functions.php to handle that.

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The best way to learn is to look at other people’s code and in the
WordPress Codex. See how they use it, how it comes together,
and of course try it yourself!
Experiment!

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M E O W W E ’ R E TA L K I N !

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Where does all of this
fit into the WP loading
process?
L E T S G E T T E C H N I C A L

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N O W Y O U ’ R E T H I N K I N G W I T H H O O K S
• Work WITH plugins as the author
intended instead of hacking them!
• GTFO WP core files!
• Build better themes, child themes,
and plugins!
• ????
• Profit!

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T H A N K S F O R C O M I N G !

24. • http://codex.wordpress.org/Plugin_API/Action_Reference
• http://code.tutsplus.com/articles/the-beginners-guide-to-
wordpress-actions-and-filters--wp-27373
• http://www.zell-weekeat.com/wordpress-actions-and-filters/
• http://codex.wordpress.org/Plugin_API/Filter_Reference
R E S O U R C E S
build create W O R D C A M P C H I C A G O