WP GraphQL register interface and to types

wp-graphql.php

<?php
/**
 * From https://wp-graphql.slack.com/archives/C3NM1M291/p1592854006371300?thread_ts=1592852289.366600&cid=C3NM1M291
 */

add_action( 'graphql_register_types', function() {
	register_graphql_interface_type( 'MyNewInterface', [
		'fields' => [
			'myNewField' => [
				'type' => 'String',
				'resolve' => function() {
					return 'resolve data...';
				}
			],
		],
	] );
	register_graphql_interfaces_to_types( [ 'MyNewInterface' ], [ 'Post' ] );
} );