add_action and add_filter in Wordpress - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to add a function to run when WordPress initializes.

Wordpress

add_action('[1]', 'my_init_function');

Drag options to blanks, or click blank then click option'

Ainit

Bwp_head

Cthe_content

Dadmin_menu

Attempts:

3 left

💡 Hint

Common Mistakes

Using a hook that runs too late like 'the_content'.

Confusing action hooks with filter hooks.

The init hook runs early in WordPress loading, perfect for initialization tasks.

2fill in blank

medium

Complete the code to modify post content using a filter.

Wordpress

add_filter('the_content', '[1]');

Drag options to blanks, or click blank then click option'

Awp_footer

Benqueue_scripts

Cmodify_content

Dadmin_init

Attempts:

3 left

💡 Hint

Common Mistakes

Using a hook name instead of a function name.

Passing a WordPress hook name instead of a function.

The function modify_content will be called to change the post content before display.

3fill in blank

hard

Fix the error in this code that tries to add an action.

Wordpress

add_action('wp_footer', [1]);

Drag options to blanks, or click blank then click option'

A'wp_footer'

Bfooter_function()

Cwp_footer

D'footer_function'

Attempts:

3 left

💡 Hint

Common Mistakes

Calling the function instead of passing its name.

Passing the hook name instead of the function name.

The function name must be passed as a string without parentheses.

4fill in blank

hard

Fill both blanks to add a filter that changes the title and set priority to 10.

Wordpress

add_filter('[1]', '[2]', 10);

Drag options to blanks, or click blank then click option'

Athe_title

Bmodify_title

Cthe_content

Dchange_title

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up content and title filters.

Using function names that don't exist.

The the_title filter changes post titles, and modify_title is the function that modifies it.

5fill in blank

hard

Fill all three blanks to add an action with a callback and priority 20.

Wordpress

add_action('[1]', '[2]', [3]);

Drag options to blanks, or click blank then click option'

Awp_enqueue_scripts

Bload_scripts

C20

Dinit

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong hook names for scripts.

Passing priority as a string instead of a number.

This adds an action on wp_enqueue_scripts to run load_scripts with priority 20.

Practice

1. What is the main purpose of add_action in WordPress?

easy

A. To create new user roles

B. To change the content of posts before display

C. To register new database tables

D. To run custom code at specific WordPress events

Solution

1. Step 1: Understand what add_action does

   add_action hooks your custom function to WordPress events so it runs at the right time.

2. Step 2: Compare with other options

   Changing content before display is for filters, not actions. Registering tables or roles is unrelated to add_action.

3. Final Answer:

   To run custom code at specific WordPress events -> Option D

4. Quick Check:

   add_action runs code on events = D [OK]

Hint: Actions run code at events; filters change data [OK]

Common Mistakes:

• Confusing add_action with add_filter
• Thinking add_action changes data directly
• Assuming add_action registers database or roles

2. Which of the following is the correct syntax to add a filter in WordPress?

easy

A. add_filter(my_function, 'the_content');

B. add_action('the_content', 'my_function');

C. add_filter('the_content', 'my_function');

D. add_action(my_function, 'the_content');

Solution

1. Step 1: Recall the correct order of parameters for add_filter

   The first parameter is the filter hook name as a string, the second is the callback function name.

2. Step 2: Check each option's parameter order and function used

   add_filter('the_content', 'my_function'); uses add_filter with correct parameter order. Options B and D use add_action incorrectly. add_filter(my_function, 'the_content'); reverses parameters.

3. Final Answer:

   add_filter('the_content', 'my_function'); -> Option C

4. Quick Check:

   Filter syntax: add_filter(hook, function) = A [OK]

Hint: Filter syntax: hook name first, function second [OK]

Common Mistakes:

• Swapping parameters order
• Using add_action instead of add_filter
• Passing function name before hook name

3. Given this code snippet:

function change_title($title) {
  return 'Hello: ' . $title;
}
add_filter('the_title', 'change_title');

What will be the output of the_title() for a post titled "World"?

medium

A. Hello: World

B. the_title

C. World

D. Hello World

Solution

1. Step 1: Understand the filter function

   The function change_title adds "Hello: " before the original title.

2. Step 2: Apply the filter to the post title

   When the_title() runs, WordPress applies the filter, so "World" becomes "Hello: World".

3. Final Answer:

   Hello: World -> Option A

4. Quick Check:

   Filter prepends 'Hello: ' to title = C [OK]

Hint: Filters modify data output; here title gets prefix [OK]

Common Mistakes:

• Ignoring the filter effect on output
• Confusing add_action with add_filter effect
• Missing the colon and space after Hello

4. What is wrong with this code?

add_filter('the_content', 'modify_content');
function modify_content() {
  return 'Modified content';
}

medium

A. The hook name is incorrect

B. The callback function must accept the content parameter

C. add_filter should be add_action here

D. The function must echo content, not return

Solution

1. Step 1: Check the callback function signature

   Filter callbacks must accept the original data as a parameter to modify it.

2. Step 2: Identify the missing parameter

   The function modify_content has no parameters, so it cannot receive the content to change.

3. Final Answer:

   The callback function must accept the content parameter -> Option B

4. Quick Check:

   Filter callbacks need input parameter = B [OK]

Hint: Filter functions must accept and return data [OK]

Common Mistakes:

• Omitting the parameter in filter callback
• Using add_action instead of add_filter
• Trying to echo instead of return in filter

5. You want to add a custom message after every post content but only for logged-in users. Which is the best way to do this using add_filter?

hard

A. Use add_filter('the_content', 'add_message'); and inside add_message check if user is logged in before appending message

B. Use add_action('the_content', 'add_message'); and append message without checking user

C. Use add_filter('the_content', 'add_message'); and always append message without user check

D. Use add_action('wp_footer', 'add_message'); to add message after content

Solution

1. Step 1: Choose the correct hook and method

   To modify post content, add_filter('the_content', ...) is correct because it changes content before display.

2. Step 2: Add user check inside callback

   To show message only to logged-in users, check user status inside the callback function before appending the message.

3. Final Answer:

   Use add_filter('the_content', 'add_message'); and inside add_message check if user is logged in before appending message -> Option A

4. Quick Check:

   Filter content + user check = A [OK]

Hint: Filter content and check user inside function [OK]

Common Mistakes:

• Using add_action instead of add_filter for content change
• Not checking user login status
• Adding message in footer instead of content