You could also try connecting to the feather with the 'nRF Connect' Android/iOS app and writing to the characteristic directly - that way you can rule out Espruino as being the problem
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.
You could also try connecting to the feather with the 'nRF Connect' Android/iOS app and writing to the characteristic directly - that way you can rule out Espruino as being the problem