Google Analytics custom element

my-ga.html

<script>
  document.registerElement('my-ga', {
   prototype: {
     __proto__: HTMLElement.prototype,
     attributeChangedCallback: function() {
       var key = this.getAttribute('key');
       if(!key) return;
       (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', key, 'auto');
       ga('send', 'pageview');

       window.addEventListener('location-changed', function() {
         ga('set', 'page', window.location.pathname);
         ga('send', 'pageview');
       });
     }
   }
 });
</script>