How to get a post thumbnail URL of a certain size

Input data:

• $post_id – ID of the post
• $size_thumb – e.g. array( 300, 300 ) or a standard / registered name like “middle” etc.

function get_thumbnail_post_url( $post_id, $size_thumb ) {
  $image_id = get_post_thumbnail_id( $post_id );
  $image_array = wp_get_attachment_image_src( $image_id, $size_thumb );
  $image_url = $image_array[0];
  return $image_url;
}

function thumbnail_post_url( $post_id, $size_thumb ) {
  echo get_thumbnail_post_url( $post_id, $size_thumb );
}

Now you can insert in a theme code like this:

<a href="<?php the_permalink(); ?>“><img decoding="async" src="<?php thumbnail_post_url( get_the_ID(), array(300, 300) ); ?>” alt=”<?php the_title(); ?>“></a>