The RxJS library's Angular module's startWith() operator is used to prepend a starting value or set of values to the start of an observable series. This operator makes sure that these initial values are released as soon as the observable is subscribed, before it starts to release its typical series of values.

Setting up
Make sure your Angular project has RxJS installed. If it's not installed already, npm can be used to add it:

Usage
Import the startWith operator from RxJS in the component or service where you want to use it:
import { startWith } from 'rxjs/operators';

Example
Let's illustrate how startWith() works with a practical example.

Service Definition
Assume you have a service that provides an observable stream of numbers:
import { Injectable } from '@angular/core';
import { Observable, interval } from 'rxjs';

@Injectable({
  providedIn: 'root'
})
export class NumberService {

  getNumbers(): Observable<number> {
    return interval(1000); // Emits incremental numbers every second
  }
}

Component Implementation
In your component, you can consume this service and use the startWith() operator to prepend an initial value before the stream of numbers starts emitting.
import { Component, OnInit } from '@angular/core';
import { NumberService } from './number.service';
import { startWith } from 'rxjs/operators';

@Component({
  selector: 'app-number-display',
  template: `
    <h2>Number Stream</h2>
    <ul>
      <li *ngFor="let number of numberStream$ | async">{{ number }}</li>
    </ul>
  `
})
export class NumberDisplayComponent implements OnInit {

  numberStream$: Observable<number>;

  constructor(private numberService: NumberService) { }

  ngOnInit(): void {
    this.numberStream$ = this.numberService.getNumbers().pipe(
      startWith(0) // Prepend 0 as the initial value
    );
  }

}

In this example

• this.numberService.getNumbers() returns an observable that emits incremental numbers every second using interval(1000).
• startWith(0) is used within the pipe() method to prepend the initial value 0 to the beginning of the observable sequence. This means that 0 will be emitted immediately upon subscription, before the interval starts emitting numbers.

Template Usage
In the component's template (number-display.component.html), subscribe to numberStream$ using the async pipe to display the emitted numbers:
<h2>Number Stream</h2>
<ul>
  <li *ngFor="let number of numberStream$ | async">{{ number }}</li>
</ul>

Google offers the Firebase Console for free hosting of your Angular application. With Firebase, you can create and expand popular apps and games that users like. endorsed by Google and relied upon by millions of companies worldwide.

Login to firebase with your google account.
https://firebase.google.com

Create Angular 17 Application using Angular CLI

As of today (May 5th, 2024) Angular 17.3.6 is the latest version.
We can upgrade our Angular CLI to latest version.

C:\Users\peter>npm install @angular/cli -g

We can upgrade the npm also
npm install -g [email protected]

We can check the Angular CLI version now.

We can create an Angular application now.
D:\Work\Angular\001>ng new AngularGlobe

After installing the packaging, we can go to the application in Visual Studio Code by Microsoft.

We can run the angular application by below command.
ng serve

We can add our globe image in app.component.html file with a small style class in app.component.css as well.

app.component.html
<h1>
  <img src="../assets/Our_Moon_Phases_and_Eclipses.gif" class="center">
</h1>
<p class="center">

  <a href="https://www.esa.int/" target="_blank">Image Courtesy : THE EUROPEAN SPACE AGENCY</a>
</p>

app.component.css
.center {
    display: block;
    margin-left: auto;
    margin-right: auto;
    width: 50%;
  }

Login Firebase Console with Google account.
We can give a name to our Angular project.

Configure google analytics.

Various options available in Firebase. You can explore each feature.

We can focus on Hosting options.

We have to install firebase-tools
npm install -g firebase-tools
firebase login

Proceed Yes

You can select the hosting option with space bar.
We have already created a project in Firebase.
Please select the project with existing project option.

Now we must select the build folder.

Before selecting the build folder we can build our project using below command.

ng build

Now we have choose the build folder.

NB: The deployment path has been modified by the Angular team to dist\<project name>\browser.

This allows us to deploy the application at this time.

Firebase Deploy

Application is deployed to https://angular-globe.web.app

If needed, you can purchase a domain from GoDaddy or BlueHost and link with Firebase free domain.