How can i declare a function as async in a Interface?

Question

I have an Interface and a Class which implements the methods, I didn't find a answer to my Problem by now. I have a function defined myAsyncFunction() in the Interface and i want to make it async :

export interface State {
  state: Class;

  myAsyncFunction(): any;
}

Answer 1

TypeScript doesn't care if a function uses the async keyword. It only cares that it is a function, what arguments it takes, and what the return value is.

The only significance of the async keyword in that context is that the function will return a promise … which will be matched by any .

Answer 2

To the caller, an async function is just a function that returns a promise:

export interface State {
  state: string;
  myAsyncFunction(): Promise<any>;
}

const state : State = {
  state: 'foo',
  myAsyncFunction: async () => 'bar'
};

Answer 3

Function is async when returns a Promise. Here is example how to define async function in interface:

interface Foo {
    bar: () => Promise<void>
}

Instead of void you can use any return type you want and of course you can use any parameters you want, for example:

interface Foo {
    bar: (test: string) => Promise<boolean>
}