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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
Yeah, the 'other' pins are all shown here, with what they're connected to (if you hover over the tags): http://www.espruino.com/Pico#pinout
Setting A9's not going to be great for the chip - it's just left available in case someone wants to use it (eg if USB isn't connected). In the absolute latest revision of the board it's actually connected via a resistor to minimize damage though.
digitalWrite won't throw an exception unless you give it an invalid pin name like "foo" - it'll just tell the hardware what to set the pin to - whether or not the hardware will actually do that or not depends on how it's set up and is pretty complex :) In the case of the IO brought out on pins it should 'just work'.