How to return promise?

Question

I have a function

parseJobs(userId: string) {
    this.getLikedJobs(userId).subscribe(result => {
        result.map(key =>{
            let rows = {
                name : (key as any).jobsUser.firstName,
                jobType: 'Liked'
            }
            let job = {...rows,...(key as any).jobPosting};
            this.result.push(job);
        });
    });

    this.getSavedJobs(userId).subscribe(result => {
        result.map(key =>{
            let rows = {
                name : (key as any).jobsUser.firstName,
                jobType: 'Saved'
            }
            let job = {...rows,...(key as any).jobPosting};
            this.result.push(job);
        });
    });
    return this.result;
}

How to return the result to promise, I tried my best, But I don't know to do t, Maybe its because of two observable I have inside of it,

Possible duplicate of [How do I return the response from an asynchronous call?](https://stackoverflow.com/questions/14220321/how-do-i-return-the-response-from-an-asynchronous-call) — Serge K., Sep 13 '17 at 09:23

score 1 · Accepted Answer · answered Sep 13 '17 at 09:52

You would promisify both observables, and then use Promise.all to get a promise that fulfils when all is done:

parseJobs(userId: string) {
    // Create a promise
    const p1 = new Promise(resolve => {
        this.getLikedJobs(userId).subscribe(result => {
            // Resolve with the modified array
            resolve(result.map(key =>{
                let rows = {
                    name : (key as any).jobsUser.firstName,
                    jobType: 'Liked'
                }
                let job = {...rows,...(key as any).jobPosting};
                // In a map, you want to return:
                return job;
            }));
        });
    });
    // Same here:
    const p2 = new Promise(resolve => {
        this.getSavedJobs(userId).subscribe(result => {
            resolve(result.map(key =>{
                let rows = {
                    name : (key as any).jobsUser.firstName,
                    jobType: 'Saved'
                }
                let job = {...rows,...(key as any).jobPosting};
                return job;
            }));
        });
    });
    // Return a promise that will fulfill when both promises fulfill
    //    and concatenate the results
    return Promise.all([p1, p2]).then(result => [].concat(...result));
}

Now you don't store the result in this.result, but make it the promised value, which you get like this:

parseJobs(1).then(result =>
    console.log(result);
});

You could of course still store the result in this.result, but that would not be best practice as it suggests that a piece of code may try to access it before it is available: you would always use the then method to get to the result.

score 0 · Answer 2 · answered Sep 13 '17 at 09:32

Maybe you need something like that:

parseJobs(userId: string): Promise<any> {
  let res: Function;
  const resPromise = new Promise((resolve: Function) => {
    // passing resolve function to upper scope
    res = resolve;
  });
  this.getLikedJobs(userId).subscribe(result => {
    ...
    // resolving result promise
    res(result);
  });
  ...
  // unresolved
  return resPromise;
}

dhilt · Answer 3 · 2017-10-05T14:46:17.010

You have 2 async calls. So there is also a single promise solution based on this knowledge.

parseJobs(userId: string) =>
  new Promise(resolve => {

    let result = [];
    const done = (job) => {
      result.push(job);
      if(result.length === 2) {
        resolve(result);
      }
    }

    this.getLikedJobs(userId).subscribe(result => {
      result.map(key =>{
        let rows = {
            name : (key as any).jobsUser.firstName,
            jobType: 'Liked'
        }
        let job = {...rows,...(key as any).jobPosting};
        done(job);
      });
    });

    this.getSavedJobs(userId).subscribe(result => {
      result.map(key =>{
        let rows = {
            name : (key as any).jobsUser.firstName,
            jobType: 'Saved'
        }
        let job = {...rows,...(key as any).jobPosting};
        done(job);
      });
    });

  });

Also you may look at Promise.all method.

How to return promise?

3 Answers3