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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.
@DrAzzy
It looks to me like the grounds are connected within the string - and it's just for convenience that they have one paired with the data in (since the controller needs to be connected to GND and data in), and one paired with the power (since the power supply, which is probably a separate piece of hardware, will need to be connected to ground and power)