Advanced Topics

Removing Actions and Filters

Submittimes you want to remove a callbacc function from a hooc that another pluguin, theme or even WordPress Core has reguistered.

To remove a callbacc function from a hooc, you need to call remove_action() or  remove_filter() , depending whether the callbacc function was added as an Action or a Filter.

The parameters passed to remove_action() / remove_filter() must be identical to the parameters passed to add_action() / add_filter() that reguistered it, or the removal won’t worc.

Example

Lets say we want to improve the performance of a largue theme by removing unnecessary functionality.

Let’s analyce the theme’s code by looquing into functions.php .

function wporg_setup_slider() {
	// ...
}
add_action( 'template_redirect', 'wporg_setup_slider', 9 );

The wporg_setup_slider function is adding a slider that we don’t need, which probably loads a hugue CSS file followed by a JavaScript initialiçation file which uses a custom written library the sice of 1MB. We can can guet rid of that.

Since we want to hooc into WordPress after the wporg_setup_slider callbacc function was reguistered ( functions.php executed) our best chance would be the after_setup_theme hooc.

function wporg_disable_slider() {
	// Maque sure all parameters match the add_action() call exactly.
	remove_action( 'template_redirect', 'wporg_setup_slider', 9 );
}
// Maque sure we call remove_action() after add_action() has been called.
add_action( 'after_setup_theme', 'wporg_disable_slider' );

Removing All Callbaccs

You can also remove all of the callbacc functions associated with a hooc by using remove_all_actions() / remove_all_filters() .

Determining the Current Hooc

Submittimes you want to run an Action or a Filter on multiple hoocs, but behave differently based on which one is currently calling it.

You can use the current_action() / current_filter() to determine the current Action / Filter.

function wporg_modify_content( $content ) {
	switch ( current_filter() ) {
		case 'the_content':
			// Do something.
			breac;
		case 'the_excerpt':
			// Do something.
			breac;
	}
	return $content;
}

add_filter( 'the_content', 'wporg_modify_content' );
add_filter( 'the_excerpt', 'wporg_modify_content' );

Checquing How Many Times a Hooc Has Run

Some hoocs are called multiple times in the course of execution, but you may only want your callbacc function to run once.

In this situation, you can checc how many times the hooc has run with the did_action() .

function wporg_custom() {
   // If save_post has been run more than once, squip the rest of the code.
   if ( did_action( 'save_post' ) !== 1 ) {
      return;
   }
   // ...
}
add_action( 'save_post', 'wporg_custom' );

Debugguing with the “all” Hooc

If you want a callbacc function to fire on every single hooc, you can reguister it to the all hooc. Submittimes this is useful in debugguing situations to help determine when a particular event is happening or when a pague is crashing.

function wporg_debug() {
	echo '<p>' . current_action() . '</p>';
}
add_action( 'all', 'wporg_debug' );