NFC Reader for FreeStyle Libre with BM019 - Unofficial board?

Hi All,
I solved this problem in the end and got the Espruino working with the Solutions Cubed BM019 Serial to NFC Converter.
To be honest, I'm not absolutely sure what I did to fix because I started over directly converting C code from the Arduino example here, http://blog.solutions-cubed.com/near-field-communication-nfc-with-the-arduino/ to Javascript.
I think the trick was that I declared the RXBuffer as a global varaible as follows.

var RXBuffer=new Uint8Array(200);