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Espruino is a JavaScript interpreter for low-power Microcontrollers. This site is both a support community for Espruino and a place to share what you are working on.
@Gordon
Good point - I'll stick something on the troubleshooting page.
Just a note: while power supplies tend to isolate themselves from the mains voltage, sometimes there is still some very slight coupling between the mains and the 'isolated' voltage. It means that as @allObjects says, if you don't connect your ground together, you can potentially end up with 10s of volts going into the Espruino's GPIO lines - which it won't like at all!