Tips for accessing the value from a subscription within a function in Ionic 3

I am working on a function that retrieves a JSON file from a specific URL. The issue I am facing is that I am trying to access a random object from this data within the file, stored in this.data. However, when I attempt to console.log(this.data) outside of the .subscribe function, it returns undefined. What steps can I take to utilize this value throughout the rest of the function and pass it to another function?

Provided below is my code snippet:

import { HttpClient } from '@angular/common/http';
import { Injectable } from '@angular/core';
import { Observable } from 'rxjs/Observable';


/*
  Generated class for the AdsProvider provider.

  See https://angular.io/guide/dependency-injection for more info on providers
  and Angular DI.
*/
@Injectable()
export class AdsProvider {
    adsUrl: string;
  constructor(public http: HttpClient) {
    console.log('Hello AdsProvider Provider');
  }
  getAds() {
    this.adsUrl = 'an url';
    console.log(this.adsUrl);
    console.log('I can get ads');
    // Requesting the file from the server
    let data: Observable<any> = this.http.get(this.adsUrl);

    data.subscribe(result => {
      this.data = result;
      // JSON file containing advertisements retrieved successfully
    });
   console.log(this.data); // This output shows as undefined
  }
}

Answer №1

When using a subscription, it operates asynchronously. Therefore, it is common for your console.log() to output 'undefined' because the console.log() function executes before the subscription returns a value.

data.subscribe(result => {
     this.data = result;
     console.log('this.data: ', this.data);

    // Call methods that work with this.data from here
});

To properly handle the data,

this.data 

needs to be processed inside the subscription. This is the standard approach in Angular - you wait for a value within a subscription and then utilize it once it becomes available.

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