How to use post_thumbnail_html filter in WordPress

post_thumbnail_html filter

Filters the post thumbnail HTML.

apply_filters( 'post_thumbnail_html', string $html, int $post_id, int $post_thumbnail_id, string|int[] $size, string|array $attr )

Description

This is filter hook , its filter the HTML of post thumbnail. Its used for rewriting the HTML output for post thumbnails.

Parameters

• $html : (string) The post thumbnail HTML.
• $post_id : (int) The post ID.
• $post_thumbnail_id : (int) The post thumbnail ID, or 0 if there isn’t one.
• $size : (string|int[]) Requested image size. Can be any registered image size name, or an array of width and height values in pixels (in that order).
• $attr : (string|array) Query string or array of attributes.

Live Example

To run the hook, copy the example below.

$html = apply_filters( 'post_thumbnail_html', $html, $post_id, $post_thumbnail_id, $size, $attr ); 
                         
if ( !empty( $html ) ) { 
                         
   // everything has led up to this point... 
                         
} 
  

The following example is for adding a hook callback.

// define the post_thumbnail_html callback 
function filter_post_thumbnail_html( $html, $post_id, $post_thumbnail_id, $size, $attr ) { 
    // make filter magic happen here... 
    return $html; 
}; 
         
// add the filter 
add_filter( 'post_thumbnail_html', 'filter_post_thumbnail_html', 10, 5 );  

To remove a hook callback, use the example below.

// remove the filter 
remove_filter( 'post_thumbnail_html', 'filter_post_thumbnail_html', 10, 5 ); 

function wpdocs_addTitleToThumbnail( $html ) {
    $id = get_post_thumbnail_id();
    $alt_text = get_post_meta( $id, '_wp_attachment_image_alt', true );
     $html = str_replace( 'alt=', 'title="' . esc_attr( $alt_text ) . '" alt=', $html );
     return $html;
}
add_filter( 'post_thumbnail_html', 'wpdocs_addTitleToThumbnail' );