async-or-sync

AsyncOrSync<Type> constructs a type with Type or PromiseLike<Type>

type AsyncOrSyncNumber = AsyncOrSync<number>;
//   ^? number | PromiseLike<number>

It's handy to use it as return type for functions in interfaces and abstract classes

interface CiProvider {
  getSHA(): AsyncOrSync<string>;
}

class Circle implements CiProvider {
  getSHA() {
    // ^? () => string
    return "abc";
  }
}

class Travis implements CiProvider {
  async getSHA() {
    // ^? () => Promise<string>
    return "def";
  }
}

TS Playground – https://tsplay.dev/wE7eZm