Add TypeScript definition

[qm3ster]

No description provided.

[limulus]

I kid you not, I was thinking I should look into doing this last night!

I’ll take a look at this later today.

[qm3ster]

It's a PR, not a feature request.
Not saying it so that you pull it faster, just so you don't end up doing the same work.
It took quite a few iterations with different arrangements of generics until it typed everything and never inferred Callback<{}>
For example, overloading the function totally didn't want to work.
Neither did making the return type a parameter, like <T, P extends Promise<T>>

[limulus]

Thanks, @qm3ster! I’m new to TypeScript, so I’m glad you did this instead of me as my first experience with TS!

I’m starting to understand how this works. After I play around with it some I expect I will pull and publish this relatively soon.