Register Comment Fielder

/**
 * Register the necessary fields to display post information correctly
 */
add_action( 'rest_api_init', 'theme_slug_register_rest_fields' );
function theme_slug_register_rest_fields() {

    register_rest_field( 'post',
        'comments',
        array(
            'get_callback' 	  => 'theme_slug_get_comments',
            'update_callback' => null,
            'schema' 		  => null,
    ) );

}

/**
 * Returns the array of comments for a given post
 *
 * @param $object
 *
 * @param $field_name
 *
 * @param $request
 *
 * @return mixed, list of comments for a post
 */
function theme_slug_get_comments( $object, $field_name, $request ) {

    return get_comments( array( 'post_id' => $object[ 'id' ] ) );

}