With TJ Holowaychuk's kind permission, I have recreated his quite beautiful Latency Tool using components written against myitcv.io/react, GopherJS bindings for React. The live hosted version can be found here:

http://blog.myitcv.io/gopherjs_examples_sites/latency/

This demo version doesn't actually check latencies for the supplied URL, instead it randomly generates values.

Here's a screenshot to whet your appetite:

The source code for the React components can be found on Github.