Angular 9 application "NgFor only supports binding to Iterables such as Arrays" error

Question

I am working on a Contacts app with Angular 9. I get a list of contacts via the following service:

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

import { Contact } from '../models/Contact';

const httpOptions = {
  headers: new HttpHeaders({
    'Content-Type': 'application/json'
  })
}

@Injectable({
  providedIn: 'root'
})

export class ContactsListService {

  contactsUrl = 'https://randomuser.me/api/?&results=500&inc=name,location,email,cell,picture';

  constructor(private http:HttpClient) { }

  getContcts():Observable<Contact[]> {
    return this.http.get<Contact[]>(`${this.contactsUrl}`);
  }

}

The Contacts List component is as follows:

import { Component, OnInit } from '@angular/core';
import { from } from 'rxjs';
import { ContactsListService } from '../../services/contacts-list.service';
import { Contact } from '../../models/Contact';

@Component({
  selector: 'app-list',
  templateUrl: './list.component.html',
})

export class ListComponent implements OnInit {

  contactsList:Contact[];

  constructor(private ContactsListService:ContactsListService) { }

  ngOnInit(): void  {
      this.ContactsListService.getContcts().subscribe(contactsList => {
        this.contactsList = contactsList;
      });

  }
}

Trying to iterate the contacts list this way

<ul *ngFor="let contact of contactsList">
    <li>{{contact.name.first}}</li>
</ul>

throws the error: Cannot find a differ supporting object '[object Object]' of type 'object'. NgFor only supports binding to Iterables such as Arrays.

That very likely means contactsList is not an array.

What am I doing wrong?

Answer 1

The URL is returning an object of the form

{
  results: [],
  info: {}
}

Use RxJS map to map the results obtained from the API.

Service

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

import { pipe } from 'rxjs';
import { map } from 'rxjs/operators';

import { Contact } from '../models/Contact';

export class ContactsListService {
  contactsUrl = 'https://randomuser.me/api/?&results=500&inc=name,location,email,cell,picture';

  constructor(private http:HttpClient) { }

  getContcts():Observable<Contact[]> {
    return this.http.get<Contact[]>(`${this.contactsUrl}`)
      .pipe(map(response => response['results']));
  }
}

Assign empty array to contactsList on declaration.

Component

import { Component, OnInit } from '@angular/core';

import { from } from 'rxjs';

import { ContactsListService } from '../../services/contacts-list.service';
import { Contact } from '../../models/Contact';

@Component({
  selector: 'app-list',
  templateUrl: './list.component.html',
})

export class ListComponent implements OnInit {
  contactsList: Contact[] = []; // assign empty array

  constructor(private ContactsListService:ContactsListService) { }

  ngOnInit(): void  {
    this.ContactsListService.getContcts().subscribe(
      contactsList => { this.contactsList = contactsList; },
      error => { // always good practice to handle error when subscribing to HTTP observables }
    );
  }
}

Answer 2

Seems like the endpoint 'https://randomuser.me/api/?&results=500&inc=name,location,email,cell,picture' does not return an array. To check it you may open it in the browser, or check in the network tab of the chrome developers tools while your app running