Honestly, I'm not sure, but looking at the source I'm pretty sure it doesn't add a CRC at any point:
@Gordon started
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.
Honestly, I'm not sure, but looking at the source I'm pretty sure it doesn't add a CRC at any point: