CODEWITHSUNDEEP
node.jspromiseasync-await
Belen
Belen

Reputation: 943

Node await Promise.all() to be fully resolved

I'm working with promises and I need to know the result of all the items processed by an async method. So I thought that a Promise.all() would solve my problem like this:

const values = await Promise.all(items.map((item) => {
  asyncMethodThatLogsAndReturnsBoolean(item);
}));

console.log(values);

What I find here is that some logs of the async method are printed after the values log. And values is printed as an array of undefined.

Is there any reason why this implementation is not waiting until all promises are resolved so the values object can be printed with the correct data?

*The asyncMethodThatLogsAndReturnsBoolean(item) calls other async methods, but all calls have await.

Upvotes: 2

Views: 4168

Answers (1)

Sal Rahman
Sal Rahman

Reputation: 4748

The callback function inside map needs to return a promise.

const values = await Promise.all(items.map((item) => {
  return asyncMethodThatLogsAndReturnsBoolean(item);
}));

Otherwise, by not explicitly returning anything, you're only returning undefined, which has Promise.all assume that the element in the mapped array has successfully "resolved" to undefined, which is not what you intended.

Upvotes: 10

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