$_GET.js

<script>
  function $_GET(name, url) {
      if (!url) {
          url = window.location.href;
      }
      name = name.replace(/[\[\]]/g, "\\$&");
      const regex = new RegExp("[?&]" + name + "(=([^&#]*)|&|#|$)");
      const results = regex.exec(url);
      if (!results) {
          return null;
      }
      if (!results[2]) {
          return '';
      }
      return decodeURIComponent(results[2].replace(/\+/g, " "));
  }
</script>
<script>
  const code = $_GET('page');
</script>