NW.js - User configuration file?

I have some global variables in my game to store game settings like stage duration, object spawn rate..etc

I would like to expose these as a configuration file, so that I can change them "on the fly" without the need to compile the game again.

What will be the recommended way to do this? JSON? XML?

I will load the JSON and XML at game start to set these values.

Thanks.

Thanks I will try this out.