Decorators are functions that modify JavaScript classes.
Angular defines a number of decorators that attach specific kinds of metadata to classes, so that the system knows what those classes mean and how they should work.
There are four main types:
Class decorators, e.g. @Component and @NgModule
Property decorators for properties inside classes, e.g. @Input and @Output
Method decorators for methods inside classes, e.g. @HostListener
Parameter decorators for parameters inside class constructors, e.g. @Inject
