After you have spent some time confused and angry you can then read the documentation of whatever library you are using and verify whether it overloads numerica

After you have spent some time confused and angry you can then read the documentation of whatever library you are using and verify whether it overloads numerical operations for its special number type or it has a function to convert them to whatever numerical type you need. In any case you wouldn't of course use UTF-8 to represent JSON numbers as it can only encode 21 bit intgers.