How to extend class type with decorator

Question

I'd like to use decorators in my project. Here's what I have written:

export const DetachedWindow = (options: TDetachedWindowOptions = defaultOptions) => <R extends Constructable>(Clazz: R): R => {
    const tmp = class extends Clazz {
        value = 'value';

        value2 = 'value2';

        constructor(...args: any[]) {
            super(...args);
            // <some logick>
        }
    };
    Object.defineProperty(tmp, 'name', { value: Clazz.name });
    return tmp;
};

As you see this decorators creates a few fields. But typescript can't recognize them

@DetachedWindow({ optA: 'optA' })
export class SomeClass {
    constructor() {
        setTimeout(() => {
            console.log(this.value); // TS2339: Property 'value' does not exist on type 'SomeClass'.
        });
    }
}

It does exsist though. If I add @ts-ignore before using these parameters, the code works okay.

I wounder, how can I create a class decorator, that would extend parent's type. I tried to do something like this:

export const DetachedWindow = (options: TDetachedWindowOptions = defaultOptions) => <R extends Constructable>(Clazz: R): R & { value: string } => {

But it didn't help.

Any ideas?

Answer 1

The answer is in the TypeScript docs of the Class decorators:

// Note that the decorator _does not_ change the TypeScript type
// and so the new property `reportingURL` is not known
// to the type system:
bug.reportingURL;
Property 'reportingURL' does not exist on type 'BugReport'.