What is the proper way to access a static property of a child class from a non-static method within the parent class?

I'm attempting to access a static property defined in a child class from a non-static method in the parent class, but I can't seem to find a way to make it work. Is this scenario possible at all?

class Parent {
    static staticList: {
        a: number
    } = {
        a: 1
    };

    public test<TParent extends Parent>(this: TParent, key: keyof TParent['constructor']['staticList']) { /** struggling to reference the constructor class of the 'this' parameter here */
        console.log(this.constructor.staticList[key]); /** although this logs the correct information, TypeScript is giving me an error - why? */
    }
}

class Child extends Parent {
    static staticList: {
        a: number
        b: number
    } = {
        a: 2,
        b: 2
    }
}

const childInstance = new Child();
childInstance.test('a'); /** this correctly logs out 2 and should suggest "a" or "b" for type hinting, not "never" */

Check out my problem on TS Playground

Answer №1

The age-old problem in TypeScript has persisted for quite some time now. The code snippet you provided is perfectly fine. To work around this issue, you can follow the solution mentioned here:

(this.constructor as typeof Parent).staticList

Another aspect to consider is the type of argument you want to use as the key for the staticList property of the current class where the argument resides. TypeScript does not support this, and I advise against attempting it because it goes against the Liskov substitution principle. Inheritance dictates that a child class's argument type must be more general, rather than more specific, than its superclass's argument type. For example, if you have code that operates on the Parent class, passing an instance of Parent or any subclass like Child should work seamlessly. However, introducing different keys in subclasses' staticList properties could lead to errors when these subclasses are passed to existing code expecting only the parent class's keys.

If you need to validate arguments based on the keys in your staticList, simply implement a check within your method to ensure that the key exists in the current statisList.

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