has_filter( string $tag, callable|bool $function_to_check = false )
Check if any filter has been registered for a hook.
Description Description
Parameters Parameters
- $tag
-
(string) (Required) The name of the filter hook.
- $function_to_check
-
(callable|bool) (Optional) The callback to check for.
Default value: false
Return Return
(false|int) If $function_to_check is omitted, returns boolean for whether the hook has anything registered. When checking a specific function, the priority of that hook is returned, or false if the function is not attached. When using the $function_to_check argument, this function may return a non-boolean value that evaluates to false (e.g.) 0, so use the === operator for testing the return value.
Source Source
File: wp-includes/plugin.php
function has_filter( $tag, $function_to_check = false ) {
global $wp_filter;
if ( ! isset( $wp_filter[ $tag ] ) ) {
return false;
}
return $wp_filter[ $tag ]->has_filter( $tag, $function_to_check );
}
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Changelog Changelog
| Version | Description |
|---|---|
| 2.5.0 | Introduced. |
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Basic Example
<?php if ( ! has_filter( 'the_content', 'example_alter_the_content' ) ) add_filter( 'the_content', 'prefix_alter_the_content' ); ?>add_filter() calls the same _wp_filter_build_unique_id() function and re-assigns the method/function parameter to the index array.
It is very likely that calling add_filter() with the same parameter list is faster than first checking if the method/function is already registered with has_filter( , ) before adding it with add_filter( , );
I am guessing the best use-case for has_filter() is to check if a filter has ANY registered methods versus checking that a specific method exists prior to re-registering it with add_filter().