On https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/async_function they say that writing
async function foo() {
return 1
}
is the same as writing
function foo() {
return Promise.resolve(1)
}
So that means that if we want to 'transform' a promise into an async function, we have to replace resolve(promise_result) with return promise_result.
But when I try to use setTimeout with async it doesn't work:
const test1 = async () => {
setTimeout(
() => {
return 5;
},
2000,
)
}
const test2 = () => new Promise(
(resolve, reject) => {
setTimeout(
() => resolve(25),
1000
)
}
)
const execute = async () => {
const result = await test1();
console.log(result); // undefined
}
execute();
If I use await on test2 it works but it doesn't work on test1. Why is that ? Is async/await only meant to deal with pending promises without using .then or can I use async with return result instead of using Promise with resolve ?
Its undefined because test1 does not return anything back. take a closer look you return it in the anonymous function back
const test1 = async () => { // <--- this function returns nothing back. Nothing means "undefined"
setTimeout(
() => { // <---- you return it here back in your anonymous function witch makes no sense
return 5;
},
2000,
)
}
That's a fun one. The problem here is that
const test1 = async () => {
setTimeout(
() => {
return 5;
},
2000,
)
}
test1 is an async function, BUT setTimeout is not.
setTimeout will just schedule whatever you pass it and return its timeoutID immediately.
In such a case, you'd really need to handle the Promise code manually.