ResultAsync is not a valid async function return type

After a lot of research into error handling in TypeScript, I’ve pretty much settled on this library as being the best option for our use. However, I am running into a major blocker. My existing codebase is built using async functions and await, but after converting the return type of a method from a Promise<something> to ResultAsync<something, someError>, the compiler complains that

Type 'typeof ResultAsync' is not a valid async function return type in ES5/ES3 because it does not refer to a Promise-compatible constructor value.

I am targeting ES5 in my tsconfig, because this is going to run in a browser, but it doesn’t make sense to me that it would not be promise compatible. This seems very basic so I figure I must be missing something here; is there a config option or something I may be overlooking? For the record, I’m using neverthrow 3.1.2.

As an example, even this basic method throws an error:

public async testAsync(): ResultAsync<string, Error> { return okAsync("Hello world!"); }

[supermacro]

Combining heterogeneous Results or ResultAsyncs has been on my todo-list for a while. In lieu of this missing functionality in neverthrow, this is how you could do it:

The combine function already does work for heterogeneous lists if you ran this code in javascript. The limitation right now is one of a simplified type definition - which forces you to only work on homogeneous lists in typescript only.

Proof: https://repl.it/@gDelgado14/heterogeneous-combine

So what you can do for now is provide typecasts on combine function invocations:

import { combine, Result } from 'neverthrow'

combine([ myOneResult, myOtherResult ]) as Result<[ Blah, Whatever ], Err1 | Err2>

If you want to get really fancy (which is what I have to implement anyways when I do get around to doing this) is to provide function overloads for all the various invocations of combine (just like how Promise.all is implemented in typescript)

[paduc]

If both func1() and func2() return ResultAsync types that you need to compare, I would create a ResultAsync that has them both and then operate the comparison.

const res = func1().andThen((value1) => func2().map((value2) =>({ value1, value2 }))) // This combines the two values in a single composite value
                   .map(({ value1, value2}) => value1 == value2) // This does the comparison