ArcGIS API for JavaScript: Building apps for Angular

Andy Gup @agup Allison Davis @araedavis

## RxJS and Observables
					
					[RxJS](https://rxjs.dev/guide/overview) (Reactive Extensions for JavaScript) - a library for reactive programming 
					
					Angular uses observables via RxJS to handle many common async operations: 
					- [HTTP](https://angular.io/guide/observables-in-angular#http) 
					- [Reactive forms](https://angular.io/guide/observables-in-angular#reactive-forms) 
					- [Router](https://angular.io/guide/observables-in-angular#router)
					
					- Under the hood, [Angular custom events extends the RxJS Subject](https://angular.io/guide/observables-in-angular#transmitting-data-between-components)

* Observables are used heavily within Angular for common async operations: http, reactive forms, routing

To learn more about Observables and their use within Angular check out Angular docs

* RxJS provides an implementation of Observables and utility functions for creating and working with them. RxJS is necessary to use Observables in JavaScript until it becomes part of the language and browsers support it.

</aside>

## [Async: Observables](https://github.com/andygup/angular-plus-arcgis-javascript-ds2020/sample_apps/async-observables)

```typescript
						this.formSubscription = this.wonderForm.valueChanges.subscribe(value => {
							// do something cool with our updated form value!
						})
						```

```typescript
						// don't forget to clean up any subscriptions
						ngOnDestroy() {
							this.formSubscription.unsubscribe()
						}
						```

<aside class="notes" data-markdown>
							* Observables provide support for passing messages between publishers and subscribers in an application

* Observables are declarative - meaning that you define a function to publish values but the function isn't executed
							until a consumer subscribes to it
							* When subscribed, the consumer then recieves notifications until the function completes, or if they unsubscribe.
							* An observable can deliver multiple values of any type
							* The observable handles set up and teardown so your app code just needs to subscribe to consume values, and when done,
							unsubscribin Whether the stream is keystrokes, response from an HTTP request, or a timer.

In code: 
							
							* so those are three ways to work with asynchronous operations in your Angular applications. Check out the samples in our github repo, a link to each demo is in the slide titles. 
						</aside>

Thank you

Andy Gup @agup

Allison Davis @araedavis