WordPress API get Post Comment

wp-api-post-comments.php

<?php

add_action( 'rest_api_init', 'theme_register_rest_fields' );
function theme_register_rest_fields() {
    register_rest_field( 'post', 'comments', array(
        'get_callback' => 'theme_get_post_comments',
        'update_callback' => null,
        'schema' => null
    ));
}

function theme_get_post_comments ( $object, $field_name, $request ) {
    return get_comments( array( 'post_id' => $object[ 'id' ] ) );
}