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

User Contributed Notes

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   Curtiss Grymala 3 years ago

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   As of WP 5.9 (as far as I can tell), the $attr parameter indicates it accepts a string or array. If you are using parameter-typing in your methods/functions, and you previously indicated that your function should expect a string, you will see fatal errors due to this (as arrays are also sent, now). The change appears to have occurred here.
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   João Carvalho 4 years ago

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   Add title attribute to post thumbnail:

   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' );