Common filter hooks in Wordpress - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to add a filter that modifies the content.

Wordpress

add_filter('the_content', '[1]');

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

Athe_title

Bwp_footer

Cinit

Dmodify_content

Attempts:

3 left

💡 Hint

Common Mistakes

Using an action hook name instead of a filter hook name.

Passing a hook name instead of a function name.

The the_content filter hook is used to modify post content before display. You need to pass the function name that will modify the content.

2fill in blank

medium

Complete the code to apply a filter to the post title.

Wordpress

add_filter('[1]', 'custom_title_filter');

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

Athe_content

Bthe_title

Cwp_head

Dinit

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'the_content' instead of 'the_title'.

Using an action hook like 'init' instead of a filter hook.

The the_title filter hook allows you to modify the post title before it is displayed.

3fill in blank

hard

Fix the error in the filter hook to modify the excerpt.

Wordpress

add_filter('the_excerpt', [1]);

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

A'modify_excerpt'

Bmodify_excerpt

C'the_excerpt'

Dthe_excerpt

Attempts:

3 left

💡 Hint

Common Mistakes

Passing the function name without quotes.

Passing the hook name instead of the function name.

The function name must be passed as a string in quotes when adding a filter.

4fill in blank

hard

Fill both blanks to create a filter that changes the widget title with priority 15.

Wordpress

add_filter('[1]', '[2]', 15);

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

Awidget_title

Bchange_widget_title

Cthe_content

Dmodify_content

Attempts:

3 left

💡 Hint

Common Mistakes

Using content-related hooks instead of widget title hooks.

Using function names that do not match the hook purpose.

The widget_title filter modifies widget titles. You must provide the function name that changes the title.

5fill in blank

hard

Fill all three blanks to add a filter that modifies comment text with priority 20 and 2 accepted arguments.

Wordpress

add_filter('[1]', '[2]', 20, [3]);

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

Acomment_text

Bmodify_comment_text

C2

D1

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong hook names like 'comment_post'.

Setting incorrect number of accepted arguments.

The comment_text filter modifies comment text. Priority 20 means it runs later, and 2 means the function accepts two arguments.

Practice

1. What is the main purpose of a filter hook in WordPress?

easy

A. To enqueue scripts and styles

B. To add new pages to the WordPress admin menu

C. To create new database tables

D. To modify data before it is displayed or saved

Solution

1. Step 1: Understand what filter hooks do

   Filter hooks allow you to change or modify data before WordPress uses or shows it.

2. Step 2: Compare options to the definition

   Only To modify data before it is displayed or saved describes modifying data before display or saving, which matches filter hooks.

3. Final Answer:

   To modify data before it is displayed or saved -> Option D

4. Quick Check:

   Filter hooks modify data = D [OK]

Hint: Filter hooks change data before use or display [OK]

Common Mistakes:

• Confusing filter hooks with action hooks
• Thinking filters add new features instead of modifying data
• Mixing up filters with script loading

2. Which of the following is the correct syntax to add a filter in WordPress?

easy

A. add_action('the_content', 'my_function');

B. add_filter('the_content', 'my_function');

C. apply_filter('the_content', 'my_function');

D. filter_add('the_content', 'my_function');

Solution

1. Step 1: Recall the correct function to add a filter

   The WordPress function to add a filter is add_filter.

2. Step 2: Check the syntax of each option

   add_filter('the_content', 'my_function'); uses add_filter with correct parameters. Others use wrong function names.

3. Final Answer:

   add_filter('the_content', 'my_function'); -> Option B

4. Quick Check:

   Use add_filter() to add filters = A [OK]

Hint: Use add_filter() to attach filter functions [OK]

Common Mistakes:

• Using add_action instead of add_filter
• Using non-existent functions like apply_filter
• Mixing up function names

3. What will be the output of this code snippet?

add_filter('the_title', function($title) {
  return strtoupper($title);
});

// Later WordPress calls apply_filters('the_title', 'Hello World');

medium

A. "HELLO WORLD"

B. "hello world"

C. "Hello World"

D. Error: Function not found

Solution

1. Step 1: Understand the filter function

   The filter changes the title by converting it to uppercase using strtoupper.

2. Step 2: Apply the filter to the input string

   When WordPress applies the filter to 'Hello World', it returns 'HELLO WORLD'.

3. Final Answer:

   "HELLO WORLD" -> Option A

4. Quick Check:

   Filter changes title to uppercase = C [OK]

Hint: Filter returns modified data, here uppercase string [OK]

Common Mistakes:

• Assuming original string is unchanged
• Confusing add_filter with add_action
• Expecting lowercase instead of uppercase

4. Identify the error in this filter hook code:

add_filter('the_content', 'modify_content');

function modify_content($content) {
  echo strtoupper($content);
}

medium

A. The filter name 'the_content' is incorrect

B. The function name must start with 'filter_'

C. The function should return the modified content, not echo it

D. add_filter requires three parameters

Solution

1. Step 1: Review the filter function behavior

   Filter functions must return the modified data, not output it directly.

2. Step 2: Check the code for return vs echo

   The function uses echo instead of return, so WordPress won't get the modified content.

3. Final Answer:

   The function should return the modified content, not echo it -> Option C

4. Quick Check:

   Filter functions must return data = B [OK]

Hint: Filter functions must return modified data, not print it [OK]

Common Mistakes:

• Using echo instead of return in filter functions
• Thinking filter names are arbitrary
• Believing add_filter always needs three parameters

5. You want to add a filter that appends " - Powered by WordPress" to every post title but only if the title is not empty. Which code correctly implements this?

hard

A. add_filter('the_title', function($title) {
if ($title !== '') {
return $title . ' - Powered by WordPress';
}
return $title;
});

B. add_filter('the_title', function($title) {
if ($title) {
echo $title . ' - Powered by WordPress';
}
});

C. add_filter('the_title', function() {
return ' - Powered by WordPress';
});

D. add_filter('the_title', function($title) {
return $title . ' - Powered by WordPress';
});

Solution

1. Step 1: Check the condition for empty title

   add_filter('the_title', function($title) { if ($title !== '') { return $title . ' - Powered by WordPress'; } return $title; }); checks if the title is not empty before appending the text, which matches the requirement.

2. Step 2: Verify the function returns the modified title

   add_filter('the_title', function($title) { if ($title !== '') { return $title . ' - Powered by WordPress'; } return $title; }); returns the modified title correctly; add_filter('the_title', function($title) { if ($title) { echo $title . ' - Powered by WordPress'; } }); uses echo which is wrong, C ignores the original title, D appends text even if title is empty.

3. Final Answer:

   code with condition and return -> Option A

4. Quick Check:

   Check empty title and return modified string = A [OK]

Hint: Return modified title only if not empty, use return not echo [OK]

Common Mistakes:

• Using echo instead of return
• Not checking if title is empty
• Replacing title instead of appending