Statamic Modifiers to add trailing slashes to URLs

TrailingSlash.php

<?php

namespace App\Modifiers;

use Statamic\Modifiers\Modifier;

class TrailingSlash extends Modifier {
  public function index($value, $params, $context) {
    // If URL is an full url or ends in /, do nothing
    if (str_starts_with($value, "http") || str_ends_with($value, "/")) {
      return $value;
    }

    // In production mode return ending slash
    if ($_ENV["APP_ENV"] == "production") {
      return "$value/";
    }

    // return default value
    return $value;
  }
}