feat: support for asynchronous factory functions

Hello!

Consider a case where you have an asynchronous factory function: for example you need to make a request or read some file from the filesystem before creating an instance of the required class.

Right now, TypeDI, if supplied with the async factory function, will add the promise object to the container instead of resolving it beforehand.

I think it’s a valid use case, but in order to implement it, we will probably need to change all container’s call signatures to async ones, which is a very drastic change in my opinion. However, this enables some very interesting functionality.

The alternative would be to just resolve those factory functions manually during the app initialization and register instances with the container, which could be non-optimal, because we don’t know if an instance some class will be actually used during program execution (sacrificing lazy-loading).

What do you think?

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The manual approach looks like this:

  const dataServiceFactory = Container.get(DataServiceFactory);
  const dataService = await dataServiceFactory.create();

  Container.set({
    type: DataService,
    value: dataService
  });

Which is somewhat cumbersome and non-automatic.

[StevenLangbroek]

Hey folks! I was wondering if this is under consideration? I think this is a very common usecase (e.g., database connections, oauth providers that open & maintain a connection), and they all need to be lifted outside of your IoC in order to be feasible.

[kgkg]

Maybe instead of changing get it would be much more user-friendly to add resolve method which will await for async factories to finish and always returns Promise?

Something like

const service = await Container.resolve(MyService);