WordPress at a glance
function is not described

wp_ajax_get_post_thumbnail_html() WP 4.6.0

Ajax handler for retrieving HTML for the featured image.

No Hooks.

Return

Nothing (null).

Usage

wp_ajax_get_post_thumbnail_html();

Code of wp ajax get post thumbnail html: wp-admin/includes/ajax-actions.php WP 5.2.2

<?php
function wp_ajax_get_post_thumbnail_html() {
	$post_ID = intval( $_POST['post_id'] );

	check_ajax_referer( "update-post_$post_ID" );

	if ( ! current_user_can( 'edit_post', $post_ID ) ) {
		wp_die( -1 );
	}

	$thumbnail_id = intval( $_POST['thumbnail_id'] );

	// For backward compatibility, -1 refers to no featured image.
	if ( -1 === $thumbnail_id ) {
		$thumbnail_id = null;
	}

	$return = _wp_post_thumbnail_html( $thumbnail_id, $post_ID );
	wp_send_json_success( $return );
}