The rule is pretty simple: if you have fields which may potentially contain integers with outside of +-2*48 range, or floating points where you care about NaNs

The rule is pretty simple: if you have fields which may potentially contain integers with outside of +-2*48 range, or floating points where you care about NaNs -- then do the safe thing and store them as strings. That one simple rule ensures your data won't be clobbered and you program won't crash. (And yes, your serialization/deserialization code will need to contain explicit string conversions. But even with that extra conversion, Javascript is way more interoperable with anything and future-proof than any alternative like protobuf or msgpack)