After encountering numerous instances of code containing the subscribe method in Angular, I began to wonder about the consequences of not utilizing them. What are we potentially missing out on?
I've noticed that all the code snippets using subscribe are written within the constructor rather than ngOnInit. Why is this practice so common?
constructor(private router: Router) {
m_Router.events.filter(event => event instanceof XComponent)
.subscribe(e => {
...
});
}
Angular's features heavily rely on observables, allowing for asynchronous code execution. Failing to subscribe to a property like m_Router.events will result in no value being returned, as an observable needs something to subscribe to.
I typically recommend placing all logic that should run when a component loads within the ngOnInit method, reserving the constructor for tasks like dependency injection. For a more detailed explanation, check out this post: Difference between Constructor and ngOnInit
Another important point about subscribers and subscriptions is that you should manually unsubscribe from them when the component unloads. While Angular handles this automatically for HttpClient subscriptions, for others like m_Router.events, you should use ngOnDestroy to unsubscribe. To do this, store the subscriber in a variable when subscribing to it.
One effective approach for subscribing to services is by utilizing the ngOnInit() lifeCycle hook method,
For more information on Angular services, you can refer to the official documentation which provides an example of a service called getHeroes:
Learn more about services here
Utilize ngOnInit for function calls It is recommended to invoke getHeroes() inside the ngOnInit lifecycle hook rather than in the constructor.
Keep the constructor simple It is advisable to keep the constructor straightforward and only use it for basic initialization tasks like assigning values to properties. The constructor should not contain any complex logic or functions that make HTTP requests to external servers.
Instead, perform the getHeroes() call within the ngOnInit lifecycle hook to ensure that it is executed at the appropriate time after creating a new instance of HeroesComponent.
ngOnInit() {
this.getHeroes();
}
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