Issue with Angular 5: Component failing to retrieve data from HttpClient Service

Question

Issue with Angular 5: Component failing to retrieve data from HttpClient Service

I'm currently utilizing Angular 5 to fetch data from JsonPlaceholder API.

Initially, I set up the service and included:

import { HttpClientModule } from '@angular/common/http';

This is the service implementation:

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

@Injectable()
export class DataService {

  private ROOT_URL = 'http://jsonplaceholder.typicode.com';

  constructor(private http: HttpClient) {}

  getPosts() {
    this.http.get(`${this.ROOT_URL}/posts`).subscribe(data => {
      return data;
    });
  }

}

Then, in my app.component.ts file:

import { Component, OnInit } from '@angular/core';
import { DataService } from '../../services/data.service';

@Component({
  selector: 'app-root',
  templateUrl: './parent.component.html',
  styleUrls: ['./parent.component.css']
})
export class AppComponent implements OnInit {

  data;

  constructor(private dataService: DataService) {

    this.data = dataService.getPosts();
    console.log(this.data);
  }

  ngOnInit() {
  }

}

However, when checking the console, it keeps displaying 'Undefined'.

Can someone please help me figure out what's wrong?

javascript angular typescript angular-services angular5

Answer 1

Answer №1

Instead of subscribing to the service, return the observable and subscribe to it within the component. This way, your data variable in the component won't be undefined as you are waiting for the http request to resolve before assigning a value.

In the service:

fetchPosts() {
    return this.http.get(`${this.API_URL}/posts`);
}

In the component:

ngOnInit() {
    this.dataService.fetchPosts().subscribe(posts => this.posts = posts);
}

Answer 2

Instead of subscribing to the service, return the observable and subscribe to it within the component. This way, your data variable in the component won't be undefined as you are waiting for the http request to resolve before assigning a value.

In the service:

fetchPosts() {
    return this.http.get(`${this.API_URL}/posts`);
}

In the component:

ngOnInit() {
    this.dataService.fetchPosts().subscribe(posts => this.posts = posts);
}

Answer 3

Answer №2

To address the issue of receiving an undefined value, it is important to note that this occurs because the data is being assigned before the http request has had a chance to resolve a value. To rectify this, consider removing the subscription from the service and relocating it to the component.

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

@Injectable()
export class DataService {
  private ROOT_URL = 'https://jsonplaceholder.typicode.com';

  constructor(private http: HttpClient) {}

  getPosts() {
    return this.http.get(`${this.ROOT_URL}/posts`);
  }
}

AppComponent.ts

import { Component } from '@angular/core';
import {DataService} from './data.service';

@Component({
  selector: 'my-app',
  templateUrl: './app.component.html',
  styleUrls: [ './app.component.css' ] 
})
export class AppComponent  {
  constructor(public data:DataService){
    this.data.getPosts().subscribe(data=>{
      console.log(data);
    })
  }
}

View the Demo here

Answer 4

To address the issue of receiving an undefined value, it is important to note that this occurs because the data is being assigned before the http request has had a chance to resolve a value. To rectify this, consider removing the subscription from the service and relocating it to the component.

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

@Injectable()
export class DataService {
  private ROOT_URL = 'https://jsonplaceholder.typicode.com';

  constructor(private http: HttpClient) {}

  getPosts() {
    return this.http.get(`${this.ROOT_URL}/posts`);
  }
}

AppComponent.ts

import { Component } from '@angular/core';
import {DataService} from './data.service';

@Component({
  selector: 'my-app',
  templateUrl: './app.component.html',
  styleUrls: [ './app.component.css' ] 
})
export class AppComponent  {
  constructor(public data:DataService){
    this.data.getPosts().subscribe(data=>{
      console.log(data);
    })
  }
}

View the Demo here

Answer 5

Answer №3

import { HttpClientModule } from '@angular/common/http';
//Below is the implementation of a service:

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

@Injectable()
export class DataService {

  private ROOT_URL = 'http://jsonplaceholder.typicode.com';

  constructor(private http: HttpClient) {}

  getPosts() {
   return this.http.get(`${this.ROOT_URL}/posts`);
  }

}
 
//app.component.ts:

import { Component, OnInit } from '@angular/core';
import { DataService } from '../../services/data.service';

@Component({
  selector: 'app-root',
  templateUrl: './parent.component.html',
  styleUrls: ['./parent.component.css']
})
export class AppComponent implements OnInit {

  data;

  constructor(private dataService: DataService) {

    this.data = dataService.getPosts();
     this.data.subscribe(data => {
       console.log(this.data;
    });
  
  }

  ngOnInit() {
  }

}

Answer 6

import { HttpClientModule } from '@angular/common/http';
//Below is the implementation of a service:

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

@Injectable()
export class DataService {

  private ROOT_URL = 'http://jsonplaceholder.typicode.com';

  constructor(private http: HttpClient) {}

  getPosts() {
   return this.http.get(`${this.ROOT_URL}/posts`);
  }

}
 
//app.component.ts:

import { Component, OnInit } from '@angular/core';
import { DataService } from '../../services/data.service';

@Component({
  selector: 'app-root',
  templateUrl: './parent.component.html',
  styleUrls: ['./parent.component.css']
})
export class AppComponent implements OnInit {

  data;

  constructor(private dataService: DataService) {

    this.data = dataService.getPosts();
     this.data.subscribe(data => {
       console.log(this.data;
    });
  
  }

  ngOnInit() {
  }

}

Answer 7

Answer №4

Instead of getting the expected return value, you are receiving nothing in return. The reason for this discrepancy is due to your placement of the return statement within a nested-lambda function. This results in the inner function returning a value, rather than the outer function which is what you actually need.

To address this issue, I recommend delving into the realm of asynchronous programming and specifically exploring Observable (which operates on a similar concept as Promise) within Angular.

Answer 8

Instead of getting the expected return value, you are receiving nothing in return. The reason for this discrepancy is due to your placement of the return statement within a nested-lambda function. This results in the inner function returning a value, rather than the outer function which is what you actually need.

To address this issue, I recommend delving into the realm of asynchronous programming and specifically exploring Observable (which operates on a similar concept as Promise) within Angular.

Answer 9

Answer №5

I completely agree with @Eduardo Vargas' response. Another effective approach could be implementing it in the resolver, which would then make the API call and insert the data into the route snapshot. This way, there is no need to wait for the page to load before subscribing in the constructor. For more information, check out:

Answer 10

I completely agree with @Eduardo Vargas' response. Another effective approach could be implementing it in the resolver, which would then make the API call and insert the data into the route snapshot. This way, there is no need to wait for the page to load before subscribing in the constructor. For more information, check out:

Issue with Angular 5: Component failing to retrieve data from HttpClient Service

Answer №1

Answer №2

Answer №3

Answer №4

Answer №5

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