wrapper for writeable property

calling jswrap_object_defineProperty expects a JS function for get/set, correct ?

Yes...

myGraphics.pixel(x,y) = newColor

Yes, that'd definitely be a job for jswrap_object_defineProperty. E.memoryMap actually does this right now: https://github.com/espruino/Espruino/blob/master/src/jswrap_espruino.c#L1697

Line 452 in jswrap_object.c

Thanks! I'll fix the docs