Tukukkk

I am trying to create a tree-like structure with inheritance like the following:

base.ts:

export class BaseClass {

    children: BaseClass = ;



    get subclassChildren(): SubClass {

        return this.children.filter((child): child is SubClass => child instanceof SubClass);

    }

}

sub.ts:

import { BaseClass } from './base';

export class SubClass extends BaseClass {}

This wont work because the base class cannot find SubClass:

TSError: ⨯ Unable to compile TypeScript:

base.ts(4,26): error TS2304: Cannot find name 'SubClass'.

base.ts(5,49): error TS2304: Cannot find name 'SubClass'.

base.ts(5,78): error TS2304: Cannot find name 'SubClass'.

Not unexpected but if I try to import the subclass in base.ts it wont work either as there are circular references to each other:

TypeError: Object prototype may only be an Object or null: undefined

Is there a way to forward declare SubClass or some other way to get this code working?

EDIT:

tsconfig.json (generated by tsc --init):

{

  "compilerOptions": {

    "target": "es5",

    "module": "commonjs",

    "strict": true,

    "esModuleInterop": true

  }

}

Try this:

base.ts:

    export class BaseClass {

        className = "base"

        children: BaseClass = ;

        get subclassChildren() {

            return this.children.filter((child) => { return child.className == "subClass" });

        }

    }

sub.ts:

import { BaseClass } from './base';

export class SubClass extends BaseClass {

    className = "subClass"

}

Using module augmentation it is possible to add methods and properties to existing classes:

base.ts:

export class BaseClass {

  children: BaseClass = ;

}

sub.ts:

import { BaseClass } from './base';



export class SubClass extends BaseClass {

    foo(){

        console.log('foo');

    }

}



/* augment base class */

declare module "./base" {

    interface BaseClass {

        subclassChildren: SubClass;

        bar(): void;

    }

}



/* implement getter */

Object.defineProperty(BaseClass.prototype, 'subclassChildren', {

    get(){

        return this.children.filter((child: BaseClass): child is SubClass => child instanceof SubClass);

    },

});



/* implement method */

BaseClass.prototype.bar = function bar(){

    console.log('bar');

}

When using it both base.ts and sub.ts has to be imported as only sub.ts contains the augmented class:

import { BaseClass } from './base';

import { SubClass } from './sub';



const root = new BaseClass();

root.children.push(new BaseClass());

root.children.push(new SubClass());



root.subclassChildren.map((child) => child.foo());

root.bar();