Angular-httpclient-unsubscribe

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1. DONT’T need to unsubscribe when using async pipe. Short ANS we DONT’T need to unsubscribe when using async pipe. export class AsyncPipeCardComponent implements OnInit { messageSubscription: Observable<string>; constructor(private upperCaseService: UpperCaseService) {} ngOnInit() { this.messageSubscription = this.upperCaseService.getUpperCaseMessage(); } } Then in the template <h4 class="card-title">{{messageSubscription | async}}</h4> The async pipe subscribes to an Observable or Promise and returns the latest value it has emitted. […]...
2. Async Pipe The async pipe subscribes to an Observable or Promise and returns the latest value it has emitted. When a new value is emitted, the async pipe marks the component to be checked for changes. When the component gets destroyed, the async pipe unsubscribes automatically to avoid potential memory leaks. Normally to render the result of […]...
3. Observables in Angular Observable isn’t an Angular specific feature, but a new standard for managing async data that will be included in the ES7 release. Angular uses observables extensively in the event system and the HTTP service. Most simply, observables are lazy collections of multiple values over time. Instead of thinking about it as a singular event or […]...
4. Streams to Components Directly One of the most important aspects of software architecture might be the concept of decoupling pieces of code. Therefore we could consider passing streams to child components as a bad practice because it creates a very tight link between the parent component and the child component. They are no longer decoupled since subscriptions in the […]...
5. Http’s Observable A very simple example usecase in an angular component file – accessControl.component.ts – which is using reselect package – I have the following @select(currentRolesListDataSelector) accessControl$: Observable<Role[]>; accessControl: Role[]; In the above, accessControl$ is name for observable , and accessControl is name for the variable And below is the way I access it inside ngOnInit() ngOnInit() { this.accessControl$.subscribe(hello => { […]...
6. Difference between the methods .pipe() and .subscribe() on a RXJS observable subscribe is not a regular operator, but a method that calls Observable’s internal subscribe function. It might be for example a function that you passed to Observable’s constructor, but most of the time it is a library implementation, which defines what will be emitted by an Observable, and when it be will emitted. This means that calling subscribe is actually […]...
7. BehaviourSubject  BehaviourSubject – Requires an initial value and emits the current value to new subscribers. One of the variants of the Subject is the BehaviorSubject. The BehaviorSubject has the characteristic that it stores the “current” value. BehaviourSubject is both an Observer and and Observable The share() operator is brought in here, so if we have multiple subscribers to this, it shares […]...
8. Converting-a-subscribe-to-asyncPipe Another use case to follow the best practice of always use async pipe when possible and only use .subscribe when side effect is an absolute necessity. Another way to think about this is, side effects in logic are hard to maintain and how prematured .subscribe forces developers to make unecessary side effects. Observable is an abstraction […]...
9. Hot vs Cold Observables Subjects are used for multicasting Observables. This means that Subjects will make sure each subscription gets the exact same value as the Observable execution is shared among the subscribers. You can do this using the Subject class. But rxjs offers different types of Subjects, namely: BehaviorSubject, ReplaySubject and AsyncSubject. Hot vs Cold Observables Cold Observables start […]...
10. Decorators-basics-in-angular A Decorator is a special kind of declaration that can be attached to a class declaration, method, accessor, property, or parameter. Decorators use the form @expression, where expression must evaluate to a function that will be called at runtime with information about the decorated declaration. For example, given the decorator @sealed we might write the sealed function […]...
11. What’s ViewChild in Angular? decorators in Angular provide a way to access and manipulate DOM elements, directives and components. In this tutorial, we’ll see an Angular 9 example of how to use the two decorators. You can use ViewChild if you need to query one element from the DOM and ViewChildren for multiple elements. In other words, they behave […]...
12. How to create an Observable of type boolean? First the wrong code that will NOT compile at all method(): Observable<boolean> { if (sessionId === '') return false; return this._http.get('sessionId=' + sessionId).map(res=> { if (res.status === "success") { return true; } return false; }); } This will give an error: Type 'boolean' is not assignable to type 'Observable'. The reason is becuase method(): Observable<boolean> […]...
13. What is Angular? Let’s see, what the angular developers have to say about that: “Angular is a platform that makes it easy to build applications with the web. Angular combines declarative templates, dependency injection, end to end tooling, and integrated best practices to solve development challenges. Angular empowers developers to build applications that live on the web, mobile, […]...
14. QueryList  QueryList is an unmodifiable list of items that Angular keeps up to date when the state of the application changes. A “QueryList,”, is a live list of directive and variable bindings contained within a directive. In laymen’s terms, its a collection of references to rendered items within the DOM (Document Object Model) tree. The QueryList is […]...
15. Route-Parameters Say we are creating an application that displays a product list. When the user clicks on a product in the list, we want to display a page showing the detailed information about that product. To do this you must: add a route parameter ID link the route to the parameter add the service that reads […]...