Generating typescript declaration files from javascript

Question

Say for example, you have a npm library, in my case mongoose, how would you go about generating d.ts files?

Answer 1

JavaScript doesn't always contain enough type information for the TypeScript compiler to infer the structures in your code - so automatically generating a definition based on JavaScript is rarely an option.

There are instructions on how to write them from scratch here:

https://www.stevefenton.co.uk/2013/01/complex-typescript-definitions-made-easy/

But there is one trick that might work (it only works in a limited set of cases).

If you paste the JavaScript into a new TypeScript file, fix any trivial errors you may get and compile it using the definition flag, it may be able to get you a file that would at least be a starting point.

tsc --declaration js.ts