Hook priority and arguments in Wordpress - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of hook priority in WordPress?

Hook priority controls the order in which functions attached to the same hook run. Lower numbers run first, higher numbers run later.

beginner

How do you specify the priority of a function attached to a WordPress hook?

You specify priority as the third argument in add_action() or add_filter(). For example: add_action('init', 'my_function', 10); where 10 is the priority.

intermediate

What does the 'accepted_args' parameter do in add_action() or add_filter()?

It tells WordPress how many arguments your hooked function can accept from the hook. This is the fourth argument in add_action() or add_filter().

intermediate

If two functions are hooked to the same action with the same priority, which one runs first?

They run in the order they were added. The function added first runs first.

beginner

Why might you want to change the priority of a hooked function?

To control when your function runs relative to others. For example, to run before or after another function hooked to the same action or filter.

What is the default priority if you don't specify one in add_action()?

A 0

B 1

C 100

D 10

The default priority in WordPress hooks is 10 if you don't specify it.

Which argument number in add_filter() sets how many arguments your function accepts?

A 3rd

B 4th

C 2nd

D 1st

The 4th argument in add_filter() or add_action() sets the number of accepted arguments.

If you want your function to run after all others hooked to the same action, what should you do?

A Use a lower priority number

B Use the default priority

C Use a higher priority number

D Remove other hooks

Higher priority numbers run later, so use a higher number to run after others.

What happens if your hooked function accepts fewer arguments than the hook provides?

A It ignores extra arguments

B WordPress stops running hooks

C It receives all arguments anyway

D It causes an error

Your function will ignore extra arguments it does not accept.

How do you hook a function to run with priority 5 and accept 2 arguments?

A add_action('hook', 'func', 5, 2);

B add_action('hook', 'func', 5);

C add_action('hook', 'func', 2, 5);

D add_action('hook', 'func', 2);

The third argument is priority (5), the fourth is accepted args (2).

Explain how hook priority affects the order of function execution in WordPress hooks.

Think about how you decide who goes first in a line.

Describe how to control the number of arguments your hooked function receives and why it matters.

Consider how many pieces of information your function needs.

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