typescript: decorator in abstract method

Question

I have the following class:

export abstract class CanDeactivateComponent {
  abstract canLeavePage(): boolean;
  abstract onPageLeave(): void;

  @someDecorator
  abstract canDeactivateBeforeUnload(): boolean;

}

and I get the error A decorator can only decorate a method implementation, not an overload. I understand I can not put a decorator in that case but, which workaround can be applied so that I force all implementations of this class to use @someDecorator before canDeactivateBeforeUnload? Isn't there any way to put this decorator in the abstract class itself so that I don't have to write it in all the implementations?

Thank you!

Answer 1

I guess it depends on the context, but perhaps using a method that proxies can work for you?

export abstract class CanDeactivateComponent {
    abstract canLeavePage(): boolean;
    abstract onPageLeave(): void;

    abstract canDeactivateBeforeUnload(): boolean;

    @someDecorator
    _canDeactivateBeforeUnload(): boolean {
        return this.canDeactivateBeforeUnload()
    }
}

Answer 2

Inspired by Rengers's answer and apokryfos's comment:

tsconfig.json:

{
  "compilerOptions": {
    "target": "ES5",
    "experimentalDecorators": true
  }
}

example.ts:

#!/usr/bin/env ts-node

export function SomeDecorator(
  target: any,
  propertyKey: string,
  descriptor: PropertyDescriptor,
) {
  console.log('SomeDecorator called');
}

export abstract class ExampleComponent {
  abstract _canDoTheThing(): boolean;

  @SomeDecorator
  canDoTheThing(): boolean {
    return this._canDoTheThing();
  }
}

class ExampleComponentImpl extends ExampleComponent {
  _canDoTheThing(): boolean {
    return true;
  }
}

new ExampleComponentImpl().canDoTheThing();

chmod u+x ./example.ts && ./example.ts

Output:

SomeDecorator called