A circular reference occurs when a base class creates a new instance of a child class within its own definition

My goal is to instantiate a child class within a static method of the base class using the following code:

class Baseclass {
    public static create(){
        const newInstance = new Childclass();
        return newInstance;
    }
}

class Childclass extends Baseclass {}

const anInstance = Baseclass.create();

This implementation behaves as expected. However, when attempting to split each class into separate files, I encounter the error:

TypeError: Class extends value undefined is not a constructor or null

An example can be viewed here. I suspect this issue is related to imports causing circular references. Despite successful execution when both classes are in the same file, I anticipate it should also function properly when separated into distinct files.

Answer №1

After some research on a GitHub issue and a related GitHub repository addressing the problem, I discovered that the solution involves using `index.ts` file like so:

export { Baseclass } from './baseclass';
// NOTE: Placing this line first causes an issue.
export { Childclass } from './childclass';

Then, you can simply reference the `index.ts` file instead of individual ones. You can check out this example for more details.

Answer №2

Placing the classes Baseclass and Childclass in separate modules results in a circular reference issue between them that cannot be resolved using ES modules; Baseclass requires Childclass to be imported for its definition, and vice versa.

The root of the problem lies with Baseclass. It should not directly reference its child class because it is meant to be independent of its descendants. If there needs to be a factory method, it can use this as the constructor in a static method. Alternatively, if base classes are not intended to be instantiated on their own, they can be marked as abstract:

abstract class Baseclass {
    public static create(){
        return new this();
    }
}

class Childclass extends Baseclass {}

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