Having trouble accessing data through Angular's subscription?

Question

Having trouble accessing data through Angular's subscription?

UPDATE How I accomplished this task is detailed below (click on the link to view my answer):

I am currently working on developing an APIService in Angular 7. My approach involves using subscribe to add data to an array that seems inaccessible through another service.

This is the method within the API service:

  getResponse(url):Observable<any> {
    return this.http.post(url, '', {responseType: 'text'});
  }

  getAll() {
      this.getResponse(this.todayApiUrl).subscribe(
        (response) => {
          this.data.push(response);
        });

      return this.data;
  }

Below is how I am attempting to invoke it in the secondary service:

export class AdsHealthService {
  today = this.callResponseApiService.getAll();


  constructor(private callResponseApiService: CallResponseApiService) { }

  getHealthValue(interval, type) {
    let obj = this.today;
    console.log(obj);
  }
}

The image attached depicts what I see when I console.log() the response. While it appears to be an array, trying to access the first element results in an undefined message. What could be the mistake in my approach? https://i.sstatic.net/NR3Ob.png

angular typescript api service

Answer 1

Answer №1

The reason for this behavior is due to the asynchronous nature of the http.post method. To convert it to a synchronous operation, you need to mark the getResponse() function as async, change the Observable to a Promise using .toPromise(), and include await before the http.post call. This adjustment ensures that getResponse() returns raw data instead of an Observable, making the .subscribe() redundant.

  async getResponse(url) {
    return await this.http.post(url, '', {responseType: 'text'}).toPromise();
  }

  async fetchAll() {
    this.data = await this.getResponse('some url');
    return this.data
  }
  async fetchData() {
    const data = await this.fetchAll();
    console.log(data);
    console.log(this.data);
  }

Answer 2

The reason for this behavior is due to the asynchronous nature of the http.post method. To convert it to a synchronous operation, you need to mark the getResponse() function as async, change the Observable to a Promise using .toPromise(), and include await before the http.post call. This adjustment ensures that getResponse() returns raw data instead of an Observable, making the .subscribe() redundant.

  async getResponse(url) {
    return await this.http.post(url, '', {responseType: 'text'}).toPromise();
  }

  async fetchAll() {
    this.data = await this.getResponse('some url');
    return this.data
  }
  async fetchData() {
    const data = await this.fetchAll();
    console.log(data);
    console.log(this.data);
  }

Answer 3

Answer №2

When utilizing your service, ensure you have the following:

  async obtainResponse(url) {
    return await this.http.post(url, '', {responseType: 'text'}).toPromise();
  }

  async fetchAllData(url) {
    return await this.obtainResponse(url);
  }

In a different service or component, you can access the promise as shown below. To guarantee receiving a promise, implement a try-catch block.

  async retrieveToday() {
    try {
      let todayData = await this.yourServiceName.fetchAllData(this.todayApiUrl);
      return todayData;
    } catch(error) {
        console.log(error);
    }
  }

Then make the call:

let info= this.yourServiceName.retrieveToday();
this.info.then((response) => {
// Handle 'response' here.
}

It is not possible to retain the value outside of the 'then' scope. To prevent unnecessary API requests, implementing a caching service is recommended to store and retrieve data when needed. For more information on caching, refer to the article at

Here is how you can manage it:

  if (!this.cacheService.has('some key')) {
    let information = this.yourServiceName.initialize();
    this.cacheService.set('some key', information)
  } else {
    let cachedData = this.cacheService.get('data');
    // Implement actions here.
  }

Trust this explanation proves helpful!

Answer 4

When utilizing your service, ensure you have the following:

  async obtainResponse(url) {
    return await this.http.post(url, '', {responseType: 'text'}).toPromise();
  }

  async fetchAllData(url) {
    return await this.obtainResponse(url);
  }

In a different service or component, you can access the promise as shown below. To guarantee receiving a promise, implement a try-catch block.

  async retrieveToday() {
    try {
      let todayData = await this.yourServiceName.fetchAllData(this.todayApiUrl);
      return todayData;
    } catch(error) {
        console.log(error);
    }
  }

Then make the call:

let info= this.yourServiceName.retrieveToday();
this.info.then((response) => {
// Handle 'response' here.
}

It is not possible to retain the value outside of the 'then' scope. To prevent unnecessary API requests, implementing a caching service is recommended to store and retrieve data when needed. For more information on caching, refer to the article at

Here is how you can manage it:

  if (!this.cacheService.has('some key')) {
    let information = this.yourServiceName.initialize();
    this.cacheService.set('some key', information)
  } else {
    let cachedData = this.cacheService.get('data');
    // Implement actions here.
  }

Trust this explanation proves helpful!

Answer 5

Answer №3

One common issue is not receiving data or receiving null or undefined values because the rest endpoint returns data in the future, but the return statement executes immediately.

Here are some ways to resolve this issue:

Use asynchronous pipe in the template and .map function in the service
Retrieve the data when it is ready in your component by using the map function

Below is an example of the code:

// A method to return data from the rest endpoint
getAll(url):Observable<any> {
   return this.http.post(url, '', {responseType: 'text'});
}

In your component class:

export class AdsHealthService {

  constructor(private callResponseApiService: CallResponseApiService) {
     this.callResponseApiService.getAll().subscribe( (today) => {
       let obj = today;
       console.log(obj);
     });
  }

 rawdata = this.callResponseApiService.getAll();


}

If you want to display the data directly in the template, you can use the async pipe.

<div>{{rawdata | async}}</div>

Answer 6

One common issue is not receiving data or receiving null or undefined values because the rest endpoint returns data in the future, but the return statement executes immediately.

Here are some ways to resolve this issue:

Use asynchronous pipe in the template and .map function in the service
Retrieve the data when it is ready in your component by using the map function

Below is an example of the code:

// A method to return data from the rest endpoint
getAll(url):Observable<any> {
   return this.http.post(url, '', {responseType: 'text'});
}

In your component class:

export class AdsHealthService {

  constructor(private callResponseApiService: CallResponseApiService) {
     this.callResponseApiService.getAll().subscribe( (today) => {
       let obj = today;
       console.log(obj);
     });
  }

 rawdata = this.callResponseApiService.getAll();


}

If you want to display the data directly in the template, you can use the async pipe.

<div>{{rawdata | async}}</div>

Answer 7

Answer №4

If you want to achieve this functionality, follow these steps:

Within your main component:

public fetchDataFromService() {
  this._api.retrieveData(this);
}

public storeData(data: any){
  this.data = data;
}

In your service file:

public retrieveData(componentObj: mainComponentModel){
    this.http.get(apiUrl).subscribe(response => componentObj.storeData(response));
}

While it may not match the exact structure of your original question, it should be easily understandable for all users.

Answer 8

If you want to achieve this functionality, follow these steps:

Within your main component:

public fetchDataFromService() {
  this._api.retrieveData(this);
}

public storeData(data: any){
  this.data = data;
}

In your service file:

public retrieveData(componentObj: mainComponentModel){
    this.http.get(apiUrl).subscribe(response => componentObj.storeData(response));
}

While it may not match the exact structure of your original question, it should be easily understandable for all users.

Having trouble accessing data through Angular's subscription?

Answer №1

Answer №2

Answer №3

Answer №4

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