gist.ts

// A.ts
abstract class A {

    public static create(t: boolean) {
        //noinspection TsLint
        const b = new D();
        return t ? new B() : new C();
    }

    abstract foo(): string
    abstract bar(): string
    con(): string {
        return 'con'
    }

}
export default A

// B.ts
import A from './A';
export default class B extends A {

    foo() {
        return 'B here';
    }

    bar(): string {
        return null;
    }
}

// D.ts
import B from './B';
const a = new B().con()