Correct Usage of Async in Typescript

Question

What is the correct usage of the async keyword in typescript? My understanding is that it is to only allow the usage of await in a function body. Specifically,

async returnPromise() : Promise<any> {} 

export const interfaceFunction() = async () {
    return returnPromise();
}

// Usage in another module
const returnValue = await interfaceFunction();

Is the interfaceFunction explicitly required to be declared as async in this case? The code works with or without the async keyword (and the return type remains a Promise in both the cases as well).

Answer 1

I'm not pretending for a full answer.

but another option that async guarantee that function returns a promise, and make result than'able. It helps much when only part of function is awaitable. see example below.

function nPromice(){
    return Promise.resolve(2);
}
async function  n(){
    if(Math.random() > 0.5 ){
        return await nPromice(); 
    } else {
        return 1;
    }
}
n().then(x => console.log(x));

Playground Link