apply_filters() │ WP 0.71

Call the functions added to a filter hook.

This function invokes all functions attached to filter hook (hook_name). It is possible to create new filter hooks by simply calling this function, specifying the name of the new hook using the (hook_name)

The function also allows for multiple additional arguments to be passed to hooks.

Example usage:

// The filter callback function.
function example_callback( $string, $arg1, $arg2 ) {
	// (maybe) modify $string.
	return $string;
}
add_filter( 'example_filter', 'example_callback', 10, 3 );
/*
 * Apply the filters by calling the 'example_callback()' function
 * that's hooked onto `example_filter` above.
 *
 * - 'example_filter' is the filter hook.
 * - 'filter me' is the value being filtered.
 * - $arg1 and $arg2 are the additional arguments passed to the callback.
$value = apply_filters( 'example_filter', 'filter me', $arg1, $arg2 );
1 time — 0.000001 sec (speed of light) | 50000 times — 0.02 sec (speed of light) | PHP 7.0.32, WP 5.0.3

No Hooks.

Return

Mixed. The filtered value after all hooked functions are applied to it.

Usage

apply_filters( $hook_name, $value );
$hook_name(string) (required)
The name of the filter hook.
$value(mixed) (required)
The value to filter.

Notes

  • Global. WP_Hook[]. $wp_filter Stores all of the filters and actions.
  • Global. String[]. $wp_current_filter Stores the list of current filters with the current one last.

Changelog

Since 0.71 Introduced.

Code of apply_filters() WP 5.9.3

wp-includes/plugin.php 
function apply_filters( $hook_name, $value ) {
	global $wp_filter, $wp_current_filter;

	$args = func_get_args();

	// Do 'all' actions first.
	if ( isset( $wp_filter['all'] ) ) {
		$wp_current_filter[] = $hook_name;
		_wp_call_all_hook( $args );
	}

	if ( ! isset( $wp_filter[ $hook_name ] ) ) {
		if ( isset( $wp_filter['all'] ) ) {
			array_pop( $wp_current_filter );
		}

		return $value;
	}

	if ( ! isset( $wp_filter['all'] ) ) {
		$wp_current_filter[] = $hook_name;
	}

	// Don't pass the tag name to WP_Hook.
	array_shift( $args );

	$filtered = $wp_filter[ $hook_name ]->apply_filters( $value, $args );

	array_pop( $wp_current_filter );

	return $filtered;
}

Filters (hooks)

Hooks (actions, filters)