----------index.html----------
<!-- Polyfills bundle. -->
<script src="src/polyfills.bundle.js" charset="utf-8"> </script>
<!-- SystemJS support. -->
<script src="src/system.bundle.js" charset="utf-8"> </script>
<!-- Import map -->
<script src="src/import-map.json" type="systemjs-importmap" charset="utf-8"> </script>
<script>
System.import('./index.js').catch(function(err) { console.error(err); })
</script>