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It'd work on any domain you like, but you need to run it on your own system.

I bet this could be used to write some very interesting Javascript-aware crawlers/scrapers.

Oh wow. Couldn't this easily be abused, if someone visited my Javascript page, that automatically entered a form under their IP?

it runs on node.js (a server side software), not a browser. So no need to worry about hijacking someones ip.