_includes/google_analytics.html

<!-- the google_analytics_id gets auto inserted from the config file -->

{% if site.google_analytics %}

<!-- Global site tag (gtag.js) - Google Analytics -->
<script async src="https://www.googletagmanager.com/gtag/js?id={{site.google_analytics}}"></script>
<script>
  window.dataLayer = window.dataLayer || [];
  function gtag(){dataLayer.push(arguments);}
  gtag('js', new Date());

  gtag('config', '{{site.google_analytics}}');
</script>

<!-- OLD SCRIPT
<script>(function(i,s,o,g,r,a,m){i['GoogleAnalyticsObject']=r;i[r]=i[r]||function(){(i[r].q=i[r].q||[]).push(arguments)},i[r].l=1*new Date();a=s.createElement(o),m=s.getElementsByTagName(o)[0];a.async=1;a.src=g;m.parentNode.insertBefore(a,m)})(window,document,'script','//www.google-analytics.com/analytics.js','ga');ga('create','{{site.google_analytics}}','auto');ga('require','displayfeatures');ga('send','pageview');</script>
-->
{% endif %}