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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
I assume this is because of your other question: http://forum.espruino.com/conversations/369336/#comment16246412
The HRM light won't turn on on its own, you need to be running something that's using HRM, like the code I gave you.