goTryRaw types are not developer friendly

[IlyaSemenov]

Consider this:

async function fn(a: number) {
  if (a < 0) {
    throw new MyError()
  }
  return otherFn(a) // known to return Promise<ComplexType>
}

const [err, data] = await goTryRaw(fn(123))

• data is typed as ComplexType, which is good.
• err is typed as unknown, which is inconvenient.

Now as I know that fn throws MyError, I want to type the return value:

const [err, data] = await goTryRaw<MyError>(fn(123))

• err is typed as MyError
• data is typed as unknown, which is inconvenient.

Sometypes ComplexType is not even exported as it may be a complex generic created inside a third party library, so it couldn't even be retrieved with ReturnType<...> escape hatch.

So basically developer is supposed to use goTryRaw without arguments and then cast error to proper type.

Ideally, there should be a way to provide error type but automatically infer return value type. I am not sure that elegant solution to this even exists, but wanted to report this concern nevertheless.

[thelinuxlich]

Hey @IlyaSemenov I agree with you! But it's not possible until TS adds this feature: microsoft/TypeScript#26242

[thelinuxlich]

What you can do is pass a second generic parameter with ComplexType:

const [err, data] = await goTryRaw<MyError, ComplexType>(fn(123))