Hook priority and arguments in Wordpress - Step-by-Step Execution

Concept Flow - Hook priority and arguments

Add Hook with Priority

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WordPress Stores Hook

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Trigger Hook Event

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WordPress Sorts Hooks by Priority

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Call Hook Functions in Order

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Pass Arguments to Hook Functions

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Functions Execute with Arguments

WordPress stores hooks with their priority and arguments, then calls them in order passing the arguments when the hook runs.

Execution Sample

Wordpress

<?php
add_action('init', 'first_hook', 10, 2);
add_action('init', 'second_hook', 5, 1);
function first_hook($arg1, $arg2) { echo "First: $arg1, $arg2"; }
function second_hook($arg1) { echo "Second: $arg1"; }
do_action('init', 'hello', 'world');
?>

This code adds two functions to the 'init' hook with different priorities and argument counts, then triggers the hook with two arguments.

Execution Table

Step	Action	Hook Name	Priority	Arguments Passed	Function Called	Output
1	Add Hook	init	10	2	first_hook	none
2	Add Hook	init	5	1	second_hook	none
3	Trigger Hook	init	N/A	['hello', 'world']	N/A	none
4	Sort Hooks by Priority	init	5 then 10	N/A	N/A	none
5	Call Hook Function	init	5	['hello']	second_hook	Second: hello
6	Call Hook Function	init	10	['hello', 'world']	first_hook	First: hello, world
7	End	init	N/A	N/A	N/A	All hooks called

💡 All hooks for 'init' called in priority order; lower number runs first.

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 4	After Step 6	Final
Hooks['init']	empty	[{func: first_hook, priority:10, args:2}]	[{func: first_hook, priority:10, args:2}, {func: second_hook, priority:5, args:1}]	[{func: second_hook, priority:5, args:1}, {func: first_hook, priority:10, args:2}]	N/A	N/A
Arguments Passed	N/A	N/A	N/A	N/A	['hello', 'world']	N/A

Key Moments - 3 Insights

Why does 'second_hook' run before 'first_hook' even though it was added later?

Because WordPress runs hooks in order of priority number, lower numbers run first. 'second_hook' has priority 5, which is before 10 of 'first_hook' (see execution_table steps 4 and 5).

Why does 'second_hook' only get one argument even though two were passed?

Because when adding the hook, it was set to accept only 1 argument. WordPress passes only as many arguments as the hook expects (see execution_table step 5).

What happens if two hooks have the same priority?

They run in the order they were added. WordPress sorts by priority first, then by order added (not shown in this example).

Visual Quiz - 3 Questions

Look at the execution table, which hook runs first when 'init' is triggered?

A first_hook

B second_hook

C both run simultaneously

D none run

💡 Hint

Check step 4 and 5 where hooks are sorted and called by priority.

At which step does WordPress sort hooks by priority?

A Step 4

B Step 3

C Step 5

D Step 6

💡 Hint

Look for the step mentioning sorting hooks by priority.

If 'first_hook' was added with priority 3, how would the execution order change?

A They run in the order added

B second_hook runs before first_hook

C first_hook runs before second_hook

D Neither runs

💡 Hint

Lower priority number means earlier execution (see concept_flow and execution_table).

Concept Snapshot

WordPress hooks run in order of priority (lower number first).
Add hooks with add_action or add_filter specifying priority and argument count.
When hook triggers, WordPress sorts hooks by priority.
Each hook function receives only the number of arguments it expects.
Hooks with same priority run in order added.

Full Transcript

In WordPress, hooks are functions attached to events. When you add a hook, you specify its priority and how many arguments it accepts. WordPress stores these hooks and when the event triggers, it sorts hooks by priority number, running lower numbers first. Then it calls each hook function, passing the arguments given by the event, but only as many as the hook expects. This way, you control the order and data each hook receives. For example, if you add two hooks to 'init' with priorities 10 and 5, the one with priority 5 runs first. If the event passes two arguments but a hook expects only one, it gets just one. Hooks with the same priority run in the order they were added.