Removing hooks in Wordpress - Step-by-Step Execution

Concept Flow - Removing hooks

Add Hook with add_action()

↓

Hook Registered in WordPress

↓

Remove Hook with remove_action()

↓

Hook Unregistered

↓

Hook Callback No Longer Runs

This flow shows how a hook is first added, then removed, so its callback stops running.

Execution Sample

Wordpress

<?php
function say_hello() {
  echo 'Hello!';
}
add_action('init', 'say_hello');
remove_action('init', 'say_hello');
?>

This code adds a hook to run say_hello on 'init', then removes it so it won't run.

Execution Table

Step	Action	Hook List State	Callback Called	Output
1	add_action('init', 'say_hello')	init: [say_hello]	No
2	WordPress fires 'init' hook	init: [say_hello]	Yes	Hello!
3	remove_action('init', 'say_hello')	init: []	No
4	WordPress fires 'init' hook again	init: []	No

💡 After remove_action, 'say_hello' is no longer in 'init' hook list, so callback does not run.

Variable Tracker

Variable	Start	After Step 1	After Step 3	Final
hook_list['init']	[]	[say_hello]	[]	[]

Key Moments - 2 Insights

Why does the callback still run if remove_action is called after add_action?

Because WordPress fires the 'init' hook before remove_action is called (see Step 2). The callback runs when the hook fires, so removing it afterward stops future runs only.

What happens if the callback name or priority differs in remove_action?

The callback won't be removed because remove_action must match the exact callback and priority used in add_action (not shown in table but important).

Visual Quiz - 3 Questions

Look at the execution table, what is the state of 'init' hook list after Step 3?

A ['say_hello', 'another_callback']

B ['say_hello']

C []

D null

💡 Hint

Check the 'Hook List State' column at Step 3.

At which step does the callback 'say_hello' run?

A Step 1

B Step 2

C Step 3

D Step 4

💡 Hint

Look at the 'Callback Called' and 'Output' columns.

If remove_action was called before add_action, what would happen?

A Callback would run once

B Callback would never run

C Callback would run twice

D Error occurs

💡 Hint

Think about the hook list state before and after add_action.

Concept Snapshot

add_action('hook', 'callback') adds a callback to a hook
remove_action('hook', 'callback') removes it
Callbacks run only if still registered when hook fires
Order matters: remove_action after hook fires stops future runs
Callback and priority must match exactly to remove

Full Transcript

This visual shows how WordPress hooks work when adding and removing callbacks. First, add_action registers a callback to a hook. When WordPress fires that hook, the callback runs. If remove_action is called after the hook fires, it removes the callback so it won't run next time. The hook list changes from having the callback to empty after removal. The callback runs only when the hook fires and the callback is registered. Matching callback names and priorities are required to remove hooks correctly.

Practice

1. What is the main purpose of using remove_action or remove_filter in WordPress?

easy

A. To stop a previously added hook from running

B. To add a new hook to WordPress

C. To create a new plugin

D. To update WordPress core files

Solution

1. Step 1: Understand what hooks do

   Hooks let you add or change WordPress features by running custom functions.

2. Step 2: Purpose of removing hooks

   Using remove_action or remove_filter stops those custom functions from running.

3. Final Answer:

   To stop a previously added hook from running -> Option A

4. Quick Check:

   Removing hooks = stopping added functions [OK]

Hint: Removing hooks stops unwanted custom functions [OK]

Common Mistakes:

• Thinking remove_action adds hooks
• Confusing remove_filter with plugin creation
• Assuming remove_action updates WordPress core

2. Which of the following is the correct syntax to remove an action hook named my_custom_action with a callback function my_function?

easy

A. remove_action('my_function', 'my_custom_action');

B. remove_action(my_custom_action, my_function);

C. remove_action('my_custom_action', 'my_function');

D. remove_action('my_custom_action');

Solution

1. Step 1: Check function parameters

   The remove_action function requires the hook name as a string and the callback function name as a string.

2. Step 2: Match correct order and quotes

   remove_action('my_custom_action', 'my_function'); correctly uses quotes and the right order: hook name first, then function name.

3. Final Answer:

   remove_action('my_custom_action', 'my_function'); -> Option C

4. Quick Check:

   Correct syntax = remove_action('hook', 'function') [OK]

Hint: Hook name first, function name second, both in quotes [OK]

Common Mistakes:

• Omitting quotes around strings
• Swapping hook and function names
• Missing the function parameter

3. Given the code below, what will be the output when the page loads?

function greet() {
  echo 'Hello!';
}
add_action('wp_footer', 'greet');
remove_action('wp_footer', 'greet');

medium

A. Hello!

B. No output

C. PHP error

D. Hello!Hello!

Solution

1. Step 1: Understand add_action effect

   The function greet is added to run on the wp_footer hook, so it would print 'Hello!'.

2. Step 2: Effect of remove_action

   Immediately after adding, remove_action stops greet from running on wp_footer.

3. Final Answer:

   No output -> Option B

4. Quick Check:

   remove_action cancels added hook = no output [OK]

Hint: Remove cancels add, so no output appears [OK]

Common Mistakes:

• Assuming add_action still runs after remove_action
• Expecting duplicate output
• Thinking code causes error

4. What is wrong with this code snippet if the goal is to remove the filter modify_title with callback change_title?

add_filter('the_title', 'change_title', 5);
remove_filter('the_title', 'change_title', 10);

medium

A. Priority missing in add_filter causes remove_filter to fail

B. remove_filter must be called before add_filter

C. Callback function name should be in double quotes

D. Priority must be the same in both add_filter and remove_filter

Solution

1. Step 1: Check priority in add_filter

   The add_filter call uses priority 5.

2. Step 2: Check priority in remove_filter

   The remove_filter specifies priority 10, which does not match.

3. Step 3: Priority must match

   To successfully remove the filter, the priority values must be identical.

4. Final Answer:

   Priority must be the same in both add_filter and remove_filter -> Option D

5. Quick Check:

   Matching priority needed to remove hook [OK]

Hint: Priority must match exactly to remove hooks [OK]

Common Mistakes:

• Ignoring priority parameter
• Calling remove_filter before add_filter
• Using wrong quotes around function name

5. You want to remove a filter added by a plugin, but your remove_filter call does not work. The plugin adds the filter like this:

add_filter('content_filter', ['PluginClass', 'modify_content'], 15);

How should you correctly remove this filter in your theme's functions.php?

hard

A. remove_filter('content_filter', ['PluginClass', 'modify_content'], 15);

B. remove_filter('content_filter', [$this, 'modify_content'], 15);

C. remove_filter('content_filter', [new PluginClass(), 'modify_content'], 15);

D. remove_filter('content_filter', 'modify_content', 15);

Solution

1. Step 1: Understand how the filter was added

   The plugin uses a class method callback: ['PluginClass', 'modify_content'] with priority 15.

2. Step 2: Remove filter requires the exact same callback

   To remove it, you must pass the identical callback array and priority.

3. Step 3: Use class name and method name array

   ['PluginClass', 'modify_content'] matches exactly; no object instance needed for class callbacks.

4. Final Answer:

   remove_filter('content_filter', ['PluginClass', 'modify_content'], 15); -> Option A

5. Quick Check:

   Remove class method filter with same array and priority [OK]

Hint: Use same class/method array and priority to remove class callbacks [OK]

Common Mistakes:

• Using function name string instead of class method array
• Ignoring priority parameter
• Passing wrong object or class name