Tips for properly waiting for forkJoin.subscribe in order to access the returned values

Question

Tips for properly waiting for forkJoin.subscribe in order to access the returned values

Continuing from this previous post, I've decided to create a new post since the question in this one is different.

Query - How can I ensure that the forkJoin operation completes before executing other business logic?

Below is the Code Snippet

export interface indexLogic {
  [id: number]: Detail;
}
async ngOnChanges(){
    await getData(); 
    // Need to guarantee that the following method only runs 
    // after this.indexLogic has been populated.
    await useInformationReceivedFromgetData(); 
}
async getData(){
  getInformations().subscribe(
    informations => {
      let subs = [];
      for (const information of informations) {
         subs.push(getOtherDetails(information.id).pipe(
            map(data => ({ id: information.id, data })) // <---
         ));
      }
        this.indexLogic = [];
          forkJoin(subs).subscribe(objects => {           
             objects.forEach(({id, data}) => { this.indexLogic.push({[id]:data}) });
          });
       }    
    );
}

javascript angular typescript rxjs

Answer 1

Answer №1

Instead of converting to a Promise, it is unnecessary in this case.

    runningParallel(subs).subscribe(results => {           
         results.forEach(({key, value}) => { this.updateList.push({[key]:value}) });
          // Add your code or function calls here
          this.performAction()
      });

Answer 2

Instead of converting to a Promise, it is unnecessary in this case.

    runningParallel(subs).subscribe(results => {           
         results.forEach(({key, value}) => { this.updateList.push({[key]:value}) });
          // Add your code or function calls here
          this.performAction()
      });

Answer 3

Answer №2

Given that the data stored in indexLogic is derived from asynchronous actions and requires immediate reaction to value changes, it is best to treat indexLogic as an asynchronous entity. Storing this information as an Observable allows for easy subscription and handling of updates.

Take a look at the code snippet below (referring to details discussed in your previous post)

interface Detail {
  id: string;
}
interface IndexLogic {
  [id: string]: Detail;
}

export class InformationComponent {
  indexLogic$ = new Observable<IndexLogic[]>();

  ngOnInit(): void {
    getInformations()
      .pipe(
        mergeMap((informations) => {
          return forkJoin(
            informations.map(({ id }) =>
              getOtherDetails(id).pipe(map((detail) => ({ [id]: detail }))),
            ),
          )
        }),
      )
      .subscribe((indexLogic) => {
        useInformationReceivedFromgetData(indexLogic)
      });
  }
}

In addition, I have repositioned the code within the ngOnInit method, which may be more suitable for initializing data retrieval in your Component rather than using ngOnChanges.

Furthermore, note that there is no usage of the async keyword in the provided code. While async/await is useful in JavaScript, leveraging Observables from RxJs eliminates the need for async/await, ensuring a consistent approach towards managing asynchronous tasks.

Answer 4

Given that the data stored in indexLogic is derived from asynchronous actions and requires immediate reaction to value changes, it is best to treat indexLogic as an asynchronous entity. Storing this information as an Observable allows for easy subscription and handling of updates.

Take a look at the code snippet below (referring to details discussed in your previous post)

interface Detail {
  id: string;
}
interface IndexLogic {
  [id: string]: Detail;
}

export class InformationComponent {
  indexLogic$ = new Observable<IndexLogic[]>();

  ngOnInit(): void {
    getInformations()
      .pipe(
        mergeMap((informations) => {
          return forkJoin(
            informations.map(({ id }) =>
              getOtherDetails(id).pipe(map((detail) => ({ [id]: detail }))),
            ),
          )
        }),
      )
      .subscribe((indexLogic) => {
        useInformationReceivedFromgetData(indexLogic)
      });
  }
}

In addition, I have repositioned the code within the ngOnInit method, which may be more suitable for initializing data retrieval in your Component rather than using ngOnChanges.

Furthermore, note that there is no usage of the async keyword in the provided code. While async/await is useful in JavaScript, leveraging Observables from RxJs eliminates the need for async/await, ensuring a consistent approach towards managing asynchronous tasks.

Answer 5

Answer №3

One way to guarantee the completion of the forkJoin operation before proceeding with other business logic is by utilizing the toPromise method and awaiting the outcome.

export interface indexLogic 
{
    [id: number]: Detail;
}

async ngOnChanges() 
{
    await this.getData();
    await this.useInformationReceivedFromgetData();
}

async getData() 
{
    const informations = await getInformations().toPromise();
    const subs = [];
    for (const information of informations) 
    {
        subs.push(getOtherDetails(information.id).pipe(
        map(data => ({ id: information.id, data }))
        ));
     }

     this.indexLogic = [];
     const objects = await forkJoin(subs).toPromise();
     objects.forEach(({ id, data }) => 
     {
          this.indexLogic.push({ [id]: data });
     });
}

async useInformationReceivedFromgetData()  
{
   // Business logic that relies on this.indexLogic being populated
}

In the modification made to the getData method, the toPromise method is now utilized instead of directly subscribing to the observable. This adjustment enables you to wait for the outcome and ensure that all asynchronous operations are concluded before proceeding. Additionally, the forkJoin operation has been transformed into a promise using toPromise to enable it to be awaited. The resulting data is stored in the objects variable, allowing the business logic within the useInformationReceivedFromgetData method to be executed securely once the this.indexLogic array has been populated.

Answer 6

One way to guarantee the completion of the forkJoin operation before proceeding with other business logic is by utilizing the toPromise method and awaiting the outcome.

export interface indexLogic 
{
    [id: number]: Detail;
}

async ngOnChanges() 
{
    await this.getData();
    await this.useInformationReceivedFromgetData();
}

async getData() 
{
    const informations = await getInformations().toPromise();
    const subs = [];
    for (const information of informations) 
    {
        subs.push(getOtherDetails(information.id).pipe(
        map(data => ({ id: information.id, data }))
        ));
     }

     this.indexLogic = [];
     const objects = await forkJoin(subs).toPromise();
     objects.forEach(({ id, data }) => 
     {
          this.indexLogic.push({ [id]: data });
     });
}

async useInformationReceivedFromgetData()  
{
   // Business logic that relies on this.indexLogic being populated
}

In the modification made to the getData method, the toPromise method is now utilized instead of directly subscribing to the observable. This adjustment enables you to wait for the outcome and ensure that all asynchronous operations are concluded before proceeding. Additionally, the forkJoin operation has been transformed into a promise using toPromise to enable it to be awaited. The resulting data is stored in the objects variable, allowing the business logic within the useInformationReceivedFromgetData method to be executed securely once the this.indexLogic array has been populated.

Tips for properly waiting for forkJoin.subscribe in order to access the returned values

Answer №1

Answer №2

Answer №3

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