I am about to install a mirror defogger (great item that I've used in a few placed while traveling).

The electrical instructions tell me to install a new junction box in the wall directly behind where the mirror will be. This new junction box will be fed from an existing lighting supply so that when the light is turned on the mirror defogger also turns on.

The defogger device is hardwired (using wire nuts) into the junction box, but then it needs to be uncovered.

My understanding of code is that all junction boxes need to be covered in case of fire caused within the box. Is this correct?

Is this acceptable, or should I put a cover on it with a hole for the wires. Or perhaps connect a plug and install a normal receptacle?

Thanks,