This is a browser variant of node-geo-tz. The original library says that the files are too big for the browser. This library takes advantage of HTTP range requests to load the data quickly. Check out the demo.
<script src="http://unpkg.com/browser-geo-tz@latest/dist/geotz.js"></script>
<script>
console.log(await GeoTZ.find(37.3861, -122.0839));
</script>
npm install browser-geo-tz
import GeoTZ from "browser-geo-tz";
console.log(await GeoTZ.find(37.3861, -122.0839));