Angular 15: How to Properly Handle Multiple HTTP Requests with RxJS and CombineLatest?
I'm working on a project and hit a roadblock. I'm attempting to set up I'm stuck on something that should probably be simple. I'm struggling with making multiple HTTP requests in my Angular 15 application and combining their responses using RxJS. I have two services that fetch data from different endpoints, and I want to show both datasets in a single component. However, I'm working with issues with how to properly manage the subscriptions and combine the results. Here's what I have so far: I created two services, `DataService1` and `DataService2`, which fetch data from different APIs: ```typescript // data-service-1.ts import { Injectable } from '@angular/core'; import { HttpClient } from '@angular/common/http'; import { Observable } from 'rxjs'; @Injectable({ providedIn: 'root' }) export class DataService1 { constructor(private http: HttpClient) { } fetchData(): Observable<any> { return this.http.get('https://api.example.com/data1'); } } // data-service-2.ts import { Injectable } from '@angular/core'; import { HttpClient } from '@angular/common/http'; import { Observable } from 'rxjs'; @Injectable({ providedIn: 'root' }) export class DataService2 { constructor(private http: HttpClient) { } fetchData(): Observable<any> { return this.http.get('https://api.example.com/data2'); } } ``` In my component, I try to use `combineLatest` to merge their outputs: ```typescript // my-component.ts import { Component, OnInit } from '@angular/core'; import { combineLatest } from 'rxjs'; import { DataService1 } from './data-service-1'; import { DataService2 } from './data-service-2'; @Component({ selector: 'app-my-component', templateUrl: './my-component.component.html' }) export class MyComponent implements OnInit { combinedData: any; constructor(private dataService1: DataService1, private dataService2: DataService2) { } ngOnInit() { combineLatest([ this.dataService1.fetchData(), this.dataService2.fetchData() ]).subscribe( ([data1, data2]) => { this.combinedData = { data1, data2 }; }, behavior => { console.behavior('behavior fetching data:', behavior); } ); } } ``` While this seems to work for the most part, I sometimes receive a `TypeError: want to read properties of undefined (reading 'data1')` when accessing `this.combinedData` in the template. I suspect this might be due to one of the HTTP calls failing. I also noticed that if either service takes too long to respond, the other one seems to time out. What is the best way to handle these scenarios in Angular using RxJS? How can I ensure that I properly manage the subscriptions and handle errors gracefully without running into undefined values? Any insights or best practices would be greatly appreciated! I'm working on a application that needs to handle this. Thanks in advance! I'm working on a CLI tool that needs to handle this. This is part of a larger REST API I'm building.