The simplest way to validate if javascript's browser is enabled. Put into the head of your page.

noscript.html

<noscript>
  <style type="text/css">
    body {
      display: none;
    }                                                                                                                                          

    html:after {
      text-align: center;
      display: block;
      font-size: 5rem;
      color: #FF0000;
      content: "Enable your javascript to use this site";
    }
  </style>
</noscript>