A little d3 colorbar, used as an example for this article http://kyrandale.com/blog/building-d3-plugin/
The easiest way to run this demo is to use a Python or nodejs one-line server:
$ python -m SimpleHTTPServer -p 8080
or, with nodejs
npm install -g http-server; http-server
Then just open up a browser and go to http://localhost:8080