Detect front-end pages only in init hook

Question

I'm trying to early exit a function within the "init" hook if it's not a front-end page. This is what I have so far, but it's definitely running on wp-json endpoints. Does anyone have a complete "early exit" clause that will ensure this is ONLY running on front-end pages?

add_action('init', 'test'); 

function test() {

    if ( is_admin || wp_doing_ajax() ) {
        return; 
    }

    // Do stuff here
}

Answer 1

I wouldn't recommend detecting that it's not the admin or REST API, because with that approach you also need to detect that it's not a WP-Cron job, an AJAX request, or the login screen.

I think it's better to test for the front end directly, with wp_using_themes(). One caveat with that, is that you still need to make sure it's not a REST API request, for reasons.

if ( wp_using_themes() && ! _tmp_is_rest_api_request() ) {
    wp_die( 'i will only run on the front end' );
}

/**
 * Returns true if the current request is for the REST API.
 *
 * @todo: Replace this once Core provides a canonical way to do this: https://core.trac.wordpress.org/ticket/42061.
 *
 * @return bool
 */
function _tmp_is_rest_api_request() {
    if ( empty( $_SERVER['REQUEST_URI'] ) ) {
        return false;
    }

    $rest_prefix = trailingslashit( rest_get_url_prefix() );

    return false !== strpos( $_SERVER['REQUEST_URI'], $rest_prefix );
}