The class "Generic" inherits from the "Events.EventEmitter

My WebStorm keeps showing the error message below repeatedly, despite my script compiling and running without any issues. Any ideas on why this is happening?

Error:(6, 9) TS2322:Type 'AnotherRandomClass' is not assignable to type 'A'.

AnotherRandomClass.ts

import * as Events from "events";

export default class AnotherRandomClass extends Events.EventEmitter {
    static instance: AnotherRandomClass;

    constructor() {
        super();
        AnotherRandomClass.instance = this;
    }

    public static getInstance(): AnotherRandomClass {
        return AnotherRandomClass.instance;
    }
}

RandomListener.ts

import * as Events from "events";
import AnotherRandomClass from "./AnotherRandomClass";

export default class RandomListener {
    public getBaseClass<A extends Events.EventEmitter>(): A {
        return AnotherRandomClass.getInstance();
    }
}

tests.ts

import AnotherRandomClass from "./AnotherRandomClass"
import RandomListener from "./RandomListener";
import * as Events from "events";

new AnotherRandomClass();

console.log(AnotherRandomClass.getInstance() instanceof Events.EventEmitter);
console.log(new RandomListener().getBaseClass());

result of tests

λ node tests.js
true
AnotherRandomClass {
  domain: null,
  _events: {},
  _eventsCount: 0,
  _maxListeners: undefined }

Answer №1

Utilizing generics may not be necessary in this scenario. By specifying that type A extends Events.EventEmitter, you are leaving the possibility for A to represent various types. Instead of using a generic parameter, it might be more straightforward to declare that getInstance returns an Events.EventEmitter.

class Base { }
class Sub extends Base {
    static instance = new Sub();
}
class Getter {
    static getClass<T extends Base>():T {
        //error Sub.instance is of type Base but not necessarily T
        return Sub.instance
    }
    static getNonGeneric(): Base {
        return Sub.instance
    }
}

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