Hook priority and arguments in Wordpress - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to add a function to a WordPress action hook with default priority.

Wordpress

add_action('init', [1]);

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

A'my_function', 5

B'my_function', 10

C'my_function'

D'my_function', 15

Attempts:

3 left

💡 Hint

Common Mistakes

Adding priority when not needed

Using incorrect quotes around function name

When adding a function to a hook, if you only provide the function name, WordPress uses the default priority 10.

2fill in blank

medium

Complete the code to add a function to a WordPress filter hook with priority 20.

Wordpress

add_filter('the_content', [1]);

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

A'modify_content', 10

B'modify_content', 5

C'modify_content'

D'modify_content', 20

Attempts:

3 left

💡 Hint

Common Mistakes

Forgetting to add priority argument

Using wrong priority number

To set a specific priority, include it as the second argument. Here, priority 20 is used.

3fill in blank

hard

Fix the error in the code to correctly specify the number of accepted arguments for the hook.

Wordpress

add_action('save_post', 'save_extra_data', 10, [1]);

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

A2

B1

C0

D3

Attempts:

3 left

💡 Hint

Common Mistakes

Setting accepted arguments to 0 disables arguments

Setting too many arguments causes errors

The fourth argument specifies how many arguments the callback accepts. For 'save_post', usually 1 argument is passed.

4fill in blank

hard

Fill all three blanks to add a filter with priority 15 and accept 2 arguments.

Wordpress

add_filter('widget_title', [1], [2], [3]);

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

A'custom_title'

B15

C2

D10

Attempts:

3 left

💡 Hint

Common Mistakes

Swapping priority and accepted arguments

Using default priority when a specific one is needed

The second argument is the function name, the third is the priority, and the fourth is the number of accepted arguments. Here, priority 15 is set.

5fill in blank

hard

Fill all three blanks to add an action with function 'log_event', priority 5, and accept 3 arguments.

Wordpress

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

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

A'log_event'

B5

C3

D10

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up the order of arguments

Using default priority instead of specified

The function name is first, then priority, then number of accepted arguments. This sets priority 5 and 3 arguments.

Practice

1. What does the priority number control when adding a function to a WordPress hook using add_action or add_filter?

easy

A. The order in which functions run on the same hook

B. The number of arguments the function accepts

C. The type of hook (action or filter)

D. The name of the hook to attach to

Solution

1. Step 1: Understand the role of priority in hooks

   Priority determines the sequence functions run when multiple functions are attached to the same hook.

2. Step 2: Differentiate priority from other parameters

   Priority is not about argument count or hook type; it only controls execution order.

3. Final Answer:

   The order in which functions run on the same hook -> Option A

4. Quick Check:

   Priority controls execution order = B [OK]

Hint: Priority sets function run order on hooks [OK]

Common Mistakes:

• Confusing priority with argument count
• Thinking priority changes hook type
• Assuming priority sets hook name

2. Which of the following is the correct syntax to add a function my_function to the init action hook with priority 15 and accepting 2 arguments?

easy

A. add_action('init', 'my_function', 2);

B. add_action('init', 'my_function', 2, 15);

C. add_action('init', my_function, 15, 2);

D. add_action('init', 'my_function', 15, 2);

Solution

1. Step 1: Recall the parameter order of add_action

   The order is hook name, function name (string), priority (default 10), and accepted arguments (default 1).

2. Step 2: Match parameters to the question

   Priority is 15, accepted arguments is 2, so the call is add_action('init', 'my_function', 15, 2);

3. Final Answer:

   add_action('init', 'my_function', 15, 2); -> Option D

4. Quick Check:

   Priority=15, args=2 syntax = D [OK]

Hint: Remember add_action(hook, func, priority, args) order [OK]

Common Mistakes:

• Swapping priority and argument count
• Omitting quotes around function name
• Passing wrong number of parameters

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

function first_func($arg) {
  return $arg . ' first';
}
function second_func($arg) {
  return $arg . ' second';
}
add_filter('test_hook', 'first_func', 20, 1);
add_filter('test_hook', 'second_func', 10, 1);
$result = apply_filters('test_hook', 'Run');
echo $result;

medium

A. Run second

B. Run first second

C. Run second first

D. Run first

Solution

1. Step 1: Understand filter execution order by priority

   Lower priority numbers run first. Here, second_func has priority 10, first_func has 20.

2. Step 2: Trace filter application

   Input 'Run' goes to second_func first, returning 'Run second'. Then 'Run second' goes to first_func, returning 'Run second first'.

3. Final Answer:

   Run second first -> Option C

4. Quick Check:

   Lower priority runs first = A [OK]

Hint: Lower priority number runs first in filters [OK]

Common Mistakes:

• Assuming higher priority runs first
• Ignoring filter chaining order
• Confusing actions and filters

4. What is wrong with this code snippet?

function my_filter($a, $b) {
  return $a + $b;
}
add_filter('calc', 'my_filter', 10, 1);
$result = apply_filters('calc', 5, 10);
echo $result;

medium

A. The priority number 10 is invalid

B. The function expects 2 arguments but only 1 is accepted in add_filter

C. apply_filters cannot pass more than one argument

D. Function name should be in double quotes

Solution

1. Step 1: Check function parameter count vs accepted args

   Function my_filter expects 2 arguments, but add_filter specifies only 1 argument accepted.

2. Step 2: Understand consequence of argument mismatch

   Only 1 argument will be passed, so $b will be undefined, causing incorrect behavior or error.

3. Final Answer:

   The function expects 2 arguments but only 1 is accepted in add_filter -> Option B

4. Quick Check:

   Accepted args must match function params = A [OK]

Hint: Match accepted args to function parameters [OK]

Common Mistakes:

• Ignoring argument count mismatch
• Thinking priority 10 is invalid
• Believing apply_filters limits arguments

5. You want to add two functions to the same filter hook modify_text. The first function should run before the second and both accept 3 arguments. Which is the correct way to add them?

hard

A. add_filter('modify_text', 'first_func', 5, 3); add_filter('modify_text', 'second_func', 10, 3);

B. add_filter('modify_text', 'first_func', 10, 3); add_filter('modify_text', 'second_func', 5, 3);

C. add_filter('modify_text', 'first_func', 3, 5); add_filter('modify_text', 'second_func', 3, 10);

D. add_filter('modify_text', 'first_func', 3); add_filter('modify_text', 'second_func', 3);

Solution

1. Step 1: Determine priority order for execution

   Lower priority number runs first, so first_func should have lower priority than second_func.

2. Step 2: Set accepted arguments correctly

   Both functions accept 3 arguments, so the fourth parameter in add_filter must be 3 for both.

3. Final Answer:

   add_filter('modify_text', 'first_func', 5, 3); add_filter('modify_text', 'second_func', 10, 3); -> Option A

4. Quick Check:

   Lower priority runs first, args=3 = C [OK]

Hint: Lower priority runs first; set args count correctly [OK]

Common Mistakes:

• Swapping priority numbers
• Setting wrong accepted argument count
• Omitting accepted arguments parameter