TS1055 when using async/await using a type alias

Question

I have declared a type alias:

export type ActivationPromise = Promise<void>;

I have written the following functions:

async function derp(): ActivationPromise {
    await test();
}

function test() : ActivationPromise {
    return Promise.resolve();
}

My tsconfig.json:

{
    "compilerOptions": {
        "noImplicitAny": true,
        "removeComments": true,
        "preserveConstEnums": true,
        "sourceMap": true,
        "module": "commonjs",
        "target": "es5",
        "allowJs": true,
        "alwaysStrict": true,
        "importHelpers": true,
        "lib": [ "dom", "es5", "es2015.promise", "es2015.iterable", "scripthost"]
    },
    "compileOnSave": false
}

When I compile, I get:

error TS1055: Type 'ActivationPromise' is not a valid async function return type in ES5/ES3 because it does not refer to a Promise-compatible constructor

If I change the return type to simply Promise<void>, the code compiles fine. Only when using the type alias, the issue happens. Since the type alias should just function as a typedef, why does this happen?

Answer 1

error TS1055: Type 'ActivationPromise' is not a valid async function return type in ES5/ES3 because it does not refer to a Promise-compatible constructor

Suggestion

Refrain from type aliasing promises 🌹

Fix

If you alias, make sure you have a value backing it as well which will be the mentioned Promise-compatible constructor instance:

export type ActivationPromise = Promise<void>;
export const ActivationPromise = Promise<void>;