It looks like a bug in the OPT3001 module, which I have now fixed. If you re-upload the code hopefully you won't get that error any more.
However it looks like the module itself hasn't been tested, so I'm afraid it may not work for you even it it does run.
Let us know what happens though - it looks promising from the numbers it is printing, so I may be able to make some tweaks at this end to fix it if it is broken.
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.
It looks like a bug in the OPT3001 module, which I have now fixed. If you re-upload the code hopefully you won't get that error any more.
However it looks like the module itself hasn't been tested, so I'm afraid it may not work for you even it it does run.
Let us know what happens though - it looks promising from the numbers it is printing, so I may be able to make some tweaks at this end to fix it if it is broken.