register_rest_field() #wcfra

register-field.php

<?php

add_action( 'rest_api_init', 'slug_register_something_random' );
function slug_register_something_random() {
    register_rest_field( 'post',
        'something',
        array(
            'get_callback'    => 'slug_get_something',
            'update_callback' => 'slug_update_something',
            'schema'          => null,
        )
    );
}