[types] input can be non object

[EdJoPaTo]

I like seeing the addition of types and type checks by the library itself!

Given that the input can be a non-object and JSON.stringify can also have a non object input, the typings should reflect that. Especially as json-stable-stringify can be more of a drop-in replacement of JSON.stringify then. (I noticed this as updating this library resulted in type errors for me as my input could be a string in some cases)

Both JSON.stringify and @types/json-stable-stringify use any for this. Which is ok for providing typings for external code but worse for type checking the actual code with typescript. any allows doing all kinds of stuff, TypeScript just assumes that its probably ok, while unknown requires you to check the types before using them (which is done by this library). So TypeScript ensures the type checks are correct.

I also added tests that ensure that non-object input actually works both in JavaScript and have working typings (without the change to unknown TypeScript is unhappy). Not sure whether they are in the correct file. Should they get their own test file?

[ljharb]

thanks! i'd caught that on the internal function but not the external one :-)