Respect do not track when loading Google Analytics

index.html

<!-- borrowing from https://stackoverflow.com/questions/950087/how-do-i-include-a-javascript-file-in-another-javascript-file -->
<script>
var ga_id = "UA-your-id-here"
function DNT () {
  if ('msDoNotTrack' in navigator) return navigator.msDoNotTrack;
  if ('doNotTrack' in window)      return window.doNotTrack;
  if ('doNotTrack' in navigator)   return navigator.doNotTrack;
  return 0;
};
function dynamicallyLoadScript(url, callback) {
  var script = document.createElement("script");
  script.src = url;
  script.type = 'text/javascript';
  script.onreadystatechange = callback;
  script.onload = callback;
  
  document.head.appendChild(script);
}
if (DNT() != 1) {
  dynamicallyLoadScript("https://www.googletagmanager.com/gtag/js?id=" + ga_id, function(){
    window.dataLayer = window.dataLayer || [];
    function gtag() { dataLayer.push(arguments); }
    gtag('js', new Date());
    gtag('config', ga_id);
  })
}
</script>