Using async/await with callback functions

Question

I'm trying to build a service layer on top of mongo. I have a User object which has an array of referenced Achievements.

After I've authenticated the user by JWT or some other means, I enter the service layer and query the relationship as follows.

findForUser(userId: string | Types.ObjectId): Promise<Achievement[]> {
  return new Promise((resolve) => {
    UserSchema.findOne({ _id: userId },
      async (err: any, user: User) => {
        const AchievementMap: Achievement[] = [];

        if (err) throw new Error(err);
        user.achievements?.forEach((a) => {
          // @ts-ignore
          AchievementMap.push(a);
        });
        resolve(AchievementMap);
      });
  });
}

What is the async/await approach to returning the result of the callback method passed into UserSchema.findOne?

Chase · Accepted Answer · 2021-01-30 14:17:49Z

3

findOne returns an awaitable object - so you don't need to pass a callback to it. Don't try mixing callbacks with async/await. The only way to return the value from the callback, as a result of the constructed promise is by using resolve (only available in the promise executor).

Instead, make it all async - functionally similar but far cleaner.

async findForUser(userId: string | Types.ObjectId): Promise<Achievement[]> {
    const user = await UserSchema.findOne({ _id: userId });

    const AchievementMap: Achievement[] = [];
    user.achievements?.forEach(a => {
        AchievementMap.push(a);
    });
    return AchievementMap;
}

answered Jan 30, 2021 at 14:17

Chase

5,6552 gold badges21 silver badges46 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Quentin · Accepted Answer · 2021-01-30 14:10:24Z

3

What is the async/await approach to returning the result of the callback

The async and await keywords are tools to manage promises. They aren't tools to manage callbacks.

The entire point of the code you have in the question is to wrap a promise based API around a function that deals in callbacks.

Now you have a promise you can await the return value of findForUser.

You can't use async and await instead of creating a promise.

answered Jan 30, 2021 at 14:10

Quentin

949k136 gold badges1.3k silver badges1.4k bronze badges

Collectives™ on Stack Overflow

Using async/await with callback functions

2 Answers 2

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related