Filter hooks in Wordpress - Step-by-Step Execution

Concept Flow - Filter hooks

WordPress runs code

↓

Apply filter hook

↓

Call all functions hooked to filter

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Each function modifies data

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Return modified data

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WordPress uses modified data

WordPress runs code and when it reaches a filter hook, it calls all functions attached to that hook to modify data before continuing.

Execution Sample

Wordpress

<?php
function add_exclamation($text) {
  return $text . '!';
}
add_filter('greeting_text', 'add_exclamation');
$text = apply_filters('greeting_text', 'Hello');
echo $text;

This code adds a filter to append an exclamation mark to the greeting text.

Execution Table

Step	Action	Input Data	Function Called	Output Data
1	apply_filters called	'Hello'	add_exclamation	'Hello!'
2	echo output	'Hello!'	none	Displays: Hello!

💡 No more functions hooked; apply_filters returns final modified data.

Variable Tracker

Variable	Start	After apply_filters	Final
$text	'Hello'	'Hello!'	'Hello!'

Key Moments - 2 Insights

Why does the original text 'Hello' change to 'Hello!'?

Because the function 'add_exclamation' hooked to 'greeting_text' filter adds '!' and returns the modified text, as shown in execution_table step 1.

What happens if no functions are hooked to a filter?

apply_filters returns the original input unchanged, since no functions modify it. This is implied by the exit_note.

Visual Quiz - 3 Questions

Look at the execution table, what is the output data after the filter function runs?

A 'Hello'

B 'Hello!'

C 'Hello!!'

D '' (empty string)

💡 Hint

Check the 'Output Data' column in step 1 of the execution_table.

At which step does the text get displayed on the screen?

A Step 2

B Step 1

C Before step 1

D After step 2

💡 Hint

Look at the 'Action' column for when echo is called in the execution_table.

If we add another function that adds '!!!' to the text, how would the output change?

A 'Hello!!!'

B 'Hello! !'

C 'Hello!!!!'

D 'Hello!'

💡 Hint

Remember each hooked function modifies the data in order, so outputs concatenate.

Concept Snapshot

Filter hooks let you change data in WordPress.
Use add_filter('hook_name', 'your_function') to attach.
Your function gets data, modifies it, returns it.
apply_filters('hook_name', data) runs all hooked functions.
Final modified data is returned and used.

Full Transcript

Filter hooks in WordPress allow you to change data before it is used. When WordPress runs code and reaches a filter hook, it calls all functions attached to that hook. Each function receives the data, changes it, and returns it. The modified data is passed to the next function or returned if none remain. For example, a function can add an exclamation mark to a greeting text. The apply_filters function runs all hooked functions and returns the final result. If no functions are hooked, the original data is returned unchanged.