Let’s break down the information specified in this decorator a bit: Make the following changes to provide the necessary information about our new service and dependencies in our application. This is done in the decorator of our main module. We’ve been using a lot of Angular “magic” but before our app is fully working we need to connect everything.
This service contains only one method to make a GET request to the. Create it by adding the following code into src/app/services/: We injected into component a service that doesn’t exist yet. You can learn more about them in the Angular documentation. This method is one of the “Angular lifecycle hooks” – methods called automatically by the Angular engine for different life stages of components such as initialization, destruction and other events. In this particular case, we need to implement the ngOnInit() method. Interfaces in TypeScript work the same way you might expect expected – if you implement it, you must implement methods declared in it. Last but not least we showed the OnInit interface and ngOnInit lifecycle methods.
The sync pipe is a special Angular mechanism to display our variable in the view template only when it is evaluated (in other words: a value is emitted by the Observable). Observables allow multiple listeners and can emit multiple values that can be manipulated using different operations such as map or filter (you can read more about it at the RxJS github page ). If you are unfamiliar with Promises, make sure to check out “A quick guide to JavaScript Promises”. Observables work similarly to Promises asynchronous types that emit values pushed to them by another function. We also used the Observable type and async pipe inside template. After that it will be automatically (almost magically) injected into our component and we will be able to reuse it later (this mechanism works similar to auto-injection in the Spring Framework). Angular will look for a class of this type and instantiate a singleton for us. If you take close look at the constructor you will see a parameter of type EchoService. Additionally, we introduced the concept of Dependency Injection.
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