In angular, we can encapsulate functionality in a component and define its interface via @Input and @Output
Interfaces in other systems typically include properties, methods and events.
It is clear how to make a property part of your interface - decorate it with @Input. It's clear how to make an event part of your interface - decorate EventEmitter with @Output It is not clear to me how to make a method part of your interface. And also how to declare events where the event handlers can return a value.
Use cases: My component is a tree-table with buttons to delete add and edit rows. It has this:
@Output() onDelete = new EventEmitter<TreeNode[]>();
this will notify the consumer that user wants to delete these nodes, but I want the consumer to be able to cancel that delete (optionally). It would be easy to do if event handlers were allowed to return values. I would declare an event where handler takes in the same parameter (TreeNode[]) and returns a Boolean. But event handlers must return void as per definition of EventEmitter's emit(e: T):void
Yes I know you can wrap the object you want to pass to a component in another object and include some boolean property in that, but to me that seems like a hack. The interface becomes unclear.
Now the case for methods:
I have in my component a method:
confirmEdit(node TreeNode)
I want the consumer of my component to be able to call this method.
How do I expose it via @Input or @Output?
Yes I know that the consumer can actually reach into my component via say @ViewChild and call any method it has, but that seems like a violation of encapsulation principle.
Is there a better way?