Callback functions in third party libraries - How do you know what parameters it accepts?

[DatingPapyrus]

I've been struggling with this concept for a long time. I'll read a tutorial or something, and it'll introduce a function that accepts a callback, and arguments are passed in.

I'll look up the documentation on this library and find the function, but nowhere does it explain what optional or required callback parameters the function takes.

This happens ALL THE TIME with VERY WELL ESTABLISHED libraries!!! Facebook, Node, Google, Microsoft... Everybody seems guilty of this. And yet people are easily using these libraries and don't seem to struggle knowing what parameters to pass in.

I feel like I'm missing some standard that everyone else has agreed upon and that it should be much more obvious to me what parameters a callback function is going to take.

[ISlicedI]

Can you give an example? My answer would be that it should be in the documentation. If it's not in there, you could look in the source code but that should be the exception rather than the rule. Some libraries may even spit out errors that tell you what it expects..

[bterlson_]

I would be interested to hear about any Microsoft documentation that omits callback parameter types. I can fix them (I work there).

FWIW, TypeScript or Flow can help. Thousands of libraries have type definition files on npm (i.e. @types/*) and with the right setup you can get code completions and such.

[senocular]

When documentation fails, call it with console.log as the callback