Angular 6 : Use of access modifier while injection any service

Question

While going through the tutorial, i am coming across a strange scenario.

while injecting the service in your component if you miss the access modifier it will give you error as given below, but adding it as private or public will run fine.

Dont we have any default scope in Angular if we miss the access modifier ?

export class UserDetailsComponent implements OnInit {

  name="";
  lastName="";
  constructor(userService : UserServiceService) { }

  ngOnInit() {
  }

  save(){
    this.userService.saveUser();

  }

}

Property 'userService' does not exist on type 'UserDetailsComponent'.

Answer 1

If you prefix a constructor parameter with an access modifier (private, protected or public) or readonly, it automatically gets "promoted" to be a class property in TypeScript. This construct is referred to as constructor parameter properties.

Without the prefix, the constructor parameter is nothing more than a method parameter, and you would have to manually assign it to a declared class property from the constructor itself.

From the handbook:

TypeScript offers special syntax for turning a constructor parameter into a class property with the same name and value. These are called parameter properties and are created by prefixing a constructor argument with one of the visibility modifiers public, private, protected, or readonly. The resulting field gets those modifier(s):