add_action and add_filter in Wordpress - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What is the output of this add_action example?

Consider this WordPress code snippet. What will be printed on the page when the 'wp_footer' action runs?

Wordpress

<?php
function show_footer_message() {
    echo '<p>Footer message here</p>';
}
add_action('wp_footer', 'show_footer_message');
?>

A Nothing is printed because 'wp_footer' is not a valid hook.

B The text '<p>Footer message here</p>' appears at the bottom of the page.

C A PHP error occurs because the function is not hooked correctly.

D The message appears at the top of the page instead of the footer.

💡 Hint

Think about when the 'wp_footer' action runs in WordPress page lifecycle.

The 'wp_footer' action runs just before the closing tag. Hooking 'show_footer_message' to it prints the message at the page bottom.

❓ state_output

intermediate

What does this add_filter code output?

Given this WordPress filter code, what will be the final title displayed?

Wordpress

<?php
function add_prefix_to_title($title) {
    return 'Prefix: ' . $title;
}
add_filter('the_title', 'add_prefix_to_title');
// Later in template:
echo apply_filters('the_title', 'Hello World');
?>

A Prefix: Hello World

B Hello World

C Prefix:

D A PHP error because apply_filters is used incorrectly.

💡 Hint

Filters modify data passed through them before output.

The filter 'add_prefix_to_title' adds 'Prefix: ' before the original title, so the output is 'Prefix: Hello World'.

📝 Syntax

advanced

Which option causes a syntax error in add_action usage?

Identify the code snippet that will cause a syntax error when hooking a function with add_action.

A add_action('init', 'my_function');

B add_action('init', function() { echo 'Hi'; });

C add_action('init', 'my_function', 10);

D add_action('init', my_function);

💡 Hint

Check if the function name is quoted as a string.

In option D, the function name is not quoted, causing a syntax error because PHP expects a string or callable.

🔧 Debug

advanced

Why does this add_filter not change the output?

This code tries to change the content but the output remains unchanged. Why?

Wordpress

<?php
function change_content($content) {
    $content = 'Changed content';
    return $content;
}
add_filter('the_content', 'change_content');
?>

A The function name is not registered correctly in add_filter.

B The filter hook 'the_content' is misspelled.

C The function does not return the modified content, so the filter has no effect.

D The filter priority is too low to affect the content.

💡 Hint

Filters must return the modified value to work.

The function modifies $content but does not return it, so the original content remains unchanged.

🧠 Conceptual

expert

Which statement correctly explains the difference between add_action and add_filter?

Choose the option that best describes how add_action and add_filter differ in WordPress.

A add_action hooks run functions at specific points without modifying data; add_filter hooks modify data by returning a value.

B add_action hooks let you modify data and must return a value; add_filter hooks only run code without returning anything.

C add_action and add_filter are interchangeable and behave the same way in WordPress.

D add_action hooks are used only for admin pages; add_filter hooks are used only for front-end pages.

💡 Hint

Think about whether the hooked function changes data or just runs code.

add_action runs code at certain points but does not expect a return value; add_filter modifies data by returning a changed value.