decorators

decorators.ts

@Injector // it says to angular that this service or class can be use without a parameter, 
automatize without parameter of constructor

example:
class ServiceOrOtherClass {
  constructor(http: httpClient) {
  }
}
Decorator is a special kind of declaration that can be attached to a class declaration, method, accessor, property, or parameter

without injector, we can't mention this service class in other classes. 
let wrongWay = ServiceOrOtherClass(http)
it is a wrong way, because we are creating many dependencies 

@Injector()
class ServiceOrOtherClass {
  constructor(http: httpClient) {
  }
  
  test() {}
}
when we use @injector, we can inject this dependence without parameter
class AnotherClass {
    constructor(private service: ServiceOrOtherClass)

    callService(): void {
        this.service.test();
    }
}

any method can be a decorator, and we can create decorators, with class decorators that save methods of a class.

public log() {

}

@log
class AnotherClass {
    constructor(private service: ServiceOrOtherClass)

    callService(): void {
        this.service.test();
    }
}

@Component, decorator that declare what html, css and title of component
@Input received something and @Output emit something