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).

It is a syntatic sugar of Promise. You don't need to declare async if your function return a Promise. You can directly await a Promise just like await an async function. If you declare your function async, you shouldn't return a Promise, otherwise you have to await twice. You should return await returnPromise(); if you really need to use a Promise from other source. — Ricky Mo
– Ricky Mo, Commented Jan 27, 2022 at 5:50

Jamiec · Accepted Answer · 2022-01-27 09:31:57Z

2

Your understanding is correct!

Is the interfaceFunction explicitly required to be declared as async in this case?

No. If you simply return a Promise you dont need to mark the method as async. Ony mark a method async if you want to await something within it.

answered Jan 27, 2022 at 9:31

Jamiec

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Mike · Accepted Answer · 2022-01-27 09:26:35Z

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));

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answered Jan 27, 2022 at 9:26

Mike

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