Hook priority and arguments in Wordpress - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What is the output order of hooks with different priorities?

Consider these WordPress hooks added to the same action 'init' with different priorities. What will be the order of output when the 'init' action runs?

Wordpress

<?php
add_action('init', function() { echo 'First'; }, 10);
add_action('init', function() { echo 'Second'; }, 5);
add_action('init', function() { echo 'Third'; }, 15);
do_action('init');
?>

A SecondThirdFirst

B SecondFirstThird

C ThirdSecondFirst

D FirstSecondThird

💡 Hint

Lower priority numbers run earlier in WordPress hooks.

Hooks with lower priority numbers run before those with higher numbers. Here, priority 5 runs first, then 10, then 15.

❓ state_output

intermediate

How many arguments does the hooked function receive?

Given this code, how many arguments will the function 'my_callback' receive when the 'save_post' action runs?

Wordpress

<?php
function my_callback($post_id, $post, $update) {
    // ...
}
add_action('save_post', 'my_callback', 10, 3);
do_action('save_post', 123, (object) ['ID' => 123], true);
?>

A 3

B 2

C 1

D 0

💡 Hint

The fourth parameter in add_action controls how many arguments are passed.

The 'add_action' call specifies 3 arguments to pass, so the function receives all three.

📝 Syntax

advanced

Which option causes a syntax error in hook registration?

Which of these add_action calls will cause a syntax error?

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

B add_action('init', 'my_function', 10, 2);

C add_action('init', 'my_function' 10, 2);

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

💡 Hint

Check for missing commas between arguments.

Option C is missing a comma between 'my_function' and 10, causing a syntax error.

🔧 Debug

advanced

Why does the hooked function not receive all arguments?

Given this code, why does 'my_callback' only receive 1 argument instead of 3?

Wordpress

<?php
function my_callback($a, $b, $c) {
    var_dump(func_get_args());
}
add_action('some_hook', 'my_callback', 10, 1);
do_action('some_hook', 1, 2, 3);
?>

A Because add_action specifies only 1 argument to pass

B Because do_action only passes 1 argument

C Because the function definition is incorrect

D Because the hook name is wrong

💡 Hint

Check the fourth parameter of add_action.

The fourth parameter of add_action controls how many arguments are passed to the callback. Here it is 1, so only one argument is passed.

🧠 Conceptual

expert

What happens if two hooks have the same priority and modify the same data?

If two functions hooked to the same filter have the same priority and both modify the input data, what determines which modification applies first?

A WordPress merges the modifications automatically

B The hook added last runs first, so its modification applies first

C Hooks with the same priority run in random order

D The hook added first runs first, so its modification applies first

💡 Hint

Think about how WordPress stores hooks internally.

When hooks have the same priority, WordPress runs them in the order they were added. The first added runs first.