TypeScript 5 - Access class constructor from a property decorator

In TypeScript 5 the property decorator's type definition has changed and there does not seem to be a way to get a class's constructor.

It now implements the TC39 proposal where the first parameter to a property decorator is always undefined:

type ClassFieldDecorator = (value: undefined, context: {
  kind: "field";
  name: string | symbol;
  access: { get(): unknown, set(value: unknown): void };
  static: boolean;
  private: boolean;
}) => (initialValue: unknown) => unknown | void;

While previously, the first parameter to the decorator function was the class's constructor:

function myPropertyDecorator(target: Object, propertyKey: string) { 
  ...
}

An ability to get a class's constructor was very useful for some libraries, e.g. validation libraries, that were operating on a class level and were storing a map of validations per class.

What are the options for doing this with the new decorator's proposal?

1. Get a class constructor in the initialization function?
2. Use experimentalDecorators instead of new decorators?
3. Something else?

You can have access to the class instance in the callback function of the decorator :

function propDecorator(value: undefined, ctx: ClassFieldDecoratorContext) {
    return function (this: any, initialValue: any) {
      console.log(this, this.constructor)
      return initialValue;
    };
}

class C {
  @propDecorator x = 1;
}

new C();

Make sure you don't use an arrow function to not keep the context of the decorator function.

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