How to we see list of libraries supported and its usage in npm package installed

Bit of background
I am a backend developer and recently started to work on web applications, starting from Wix.
In my work style, whenever we install a new package, we check the list of library functions supported, its parameters, exceptions, response.

Coming to my experience in Wix:
Wix inbuilt packages documents work pretty much the same, I click on the imported package and it takes me to the library and there we get the good document by Velo.

Problem Statement:
But when I install an npm package, eg: node-fs. I couldn’t figure out a way to see what are the library functions supported by this, and how to use it.
I check the official site(I believe) which is https://www.npmjs.com/package/node-fs, but it wasn’t of any help.

Kindly provide me some leads to make progress in this line.