How to Unhook a Function From a Filter in WordPress

Background

WordPress filters are a mechanism to allow the replacement of values produced by the code being run. A filter consists of a name and a set of callbacks. Triggering a filter means executing all callbacks hooked to the filter.

In some cases, a function hooked to a filter causes an undesired result when the filter is triggered. In other cases, the hooking is unnecessary.

Syntax

remove_filter($tag, $function, $priority) removes the function $function from the set of callbacks of the $tag filter. $priority is the current priority of $function within the set of callbacks. If $priority is not specified, it takes a value of 10. The result is TRUE if the function was successfully removed, otherwise FALSE.

Keep in mind these tips to avoid common errors:

• $priority must match the priority specified in the add_filter call that hooked the function to the filter
• remove_filter must be executed after the corresponding add_filter call

Example

By default, WordPress replaces double line breaks in the post content with <p> elements. It happens because the WordPress Core hooks the function wpautop to the 'the_content' filter.

Follow this procedure to disable the previous behavior. It is adaptable to any filter/function pair.

Step 1: Find where the function is hooked to the filter in the codebase.

The function add_filter hooks a function to a filter in WordPress. Open the search feature of the IDE and find occurrences of the text 'wpautop' in the codebase. Go to the occurrence where the text appears in a call to add_filter and 'the_content' is the target filter. You will find that this occurrence is in the file default-filters.php.

add_filter('the_content', 'wpautop');

Step 2: Unhook the function from the filter.

Copy the previous statement to a location executed later. Replace add_filter with remove_filter.

remove_filter('the_content', 'wpautop');

Step 3: Test.

Visit a post containing double line breaks in the post content and verify that they were not converted to <p> elements. Note that this conversion never happens if you are using the block editor.

Further reading

I recommend the other tutorials in this series to learn more about filters in WordPress.

Source code

The source code developed in this tutorial, including a possible answer to the exercise, is available here.