Is there a way I can import types using a generic parameter?

Question

I have a function that works a bit like a wrapper for dynamic import() syntax:

async importWrapper(url) {
  return await import(url);
}

Is there a way I can make this function use a return type based on the value of the url parameter?

I tried:

async function importWrapper<T extends string>(url: T) : Promise<typeof import(T)> {
    return await import(url);
}

but this gives an error:

Promise<typeof import(T)>
//                   ^^^--- TS1141 String literal expected

playground

Answer 1

It is not possible, at least as of TypeScript 4.6, to express "import types" of a form like import(T) or typeof import(T).

There is an open feature request at microsoft/TypeScript#44636 asking for support for something like this. It is currently marked as "Awaiting Feedback" which means they would like to see what the community thinks before considering adopting such a feature. So you might want to give the issue a 👍 and comment on your use case; specifically why you need this and why existing workarounds don't suffice.

In any case I wouldn't expect to see anything implemented soon, or maybe even ever. A comment by the dev lead for TS says that it would be a "heavy lift" to implement. Oh well!