Fun tweet from a while ago now that highlights the fun to be had by having side-effects hanging off a GET rather than a POST; from a time when it more or less still wasn't quite the issue it ended up being.
Site that sort of provides active JavaScript notebooks, with a view to doing most/all of the work on the client side. I was sort of hoping there'd be a self-host option or something and I'm not seeing that. On the other hand it could be a good tool for tinkering with and prototyping code.