异步等待 promise.all 映射未解决承诺

Question

i'm trying to understand Promise.all in a map function using async await but i seem to returning promises which are pending, i don't understand why

Here is the working code when i have a .then to resolve my promise

const arr = [1, 2, 3, 4, 5];

const results = Promise.all(arr.map( item => {
    return item + 1;
}));

results.then(result=> console.log(result))

which logs as expected = [ 2, 3, 4, 5, 6 ]

now to implement the function using async-await i know i need to wrap the function in an async function with the keyword async and await for promise.all

const results = async () => await Promise.all(arr.map(async (item) => {
    return item + 1;
}));


console.log(results())

but i always seem to log Promise { <pending> } I don't understand what im doing wrong

Answer 1

Using asnyc / await doesn't make the results function synchronous. (It's literally tagged as async !) So it returns a promise, and you have to await that before logging the values:

 const arr = [1, 2, 3]; const results = Promise.all( arr.map(async item => item + 1) ); (async () => { console.log(await results) })();

Answer 2

What you are doing is assigning an async function to results, thats not how await for the asynchronous function works. You need to assign a promise to results and to avoid then callback chaining we can use async/await to get the response.

 const arr = [1, 2, 3]; const results = Promise.all(arr.map(async (item) => { return item + 1; })); async function output () { console.log(await results); } output();

Answer 3

Like other answers have mentioned, async returns a promise. Thats the reason you are getting

 Promise { <pending> } 

Irrespective of whether what you are doing makes sense, you could just use then on this promise that was returned like so

 const results = async () => await Promise.all( [1, 2, 3, 4, 5].map(async item => { return item + 1; }) ); results().then(e => console.log(e));