Typescript generics using class constructor that extends another class with static property inside a factory function

Question

Trying to extend a class with a static property, but I'm getting the following type error:

Property 'property' does not exist on type 'new (...args: any[]) => T'.(2339)

class A {
    static property = 'a'
}

class B extends A {}

function factory<T extends A>(type: new (...args: any[]) => T): T {
    if (type.property) { // error -> Property 'property' does not exist on type 'new (...args: any[]) => T'.(2339)
        console.log('heyyyyy')
    }

    return new type();
}

const b = factory(B);

console.log(B.property)

What must be done for this to work without the type error?

Thank you for your help.

Lesiak · Accepted Answer · 2020-08-19 19:25:12Z

2

To extend the answer by @mpstv (and avoid type cast)

type Constructor = new (...args: any) => any;

function factory<T extends typeof A & Constructor>(type: T): InstanceType<T> {
  if (type.property) {
    console.log('heyyyyy');
  }

  return new type();
}

answered Aug 19, 2020 at 19:25

Lesiak

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mpstv · Accepted Answer · 2020-08-19 19:11:27Z

1

The answer to this question is here https://stackoverflow.com/a/49784147/14132148

Your factory will look like:

function factory<T extends typeof A>(type: T): InstanceType<T> {
  if (type.property) {
    console.log('heyyyyy');
  }

  return new type() as InstanceType<T>;
}

answered Aug 19, 2020 at 19:11

mpstv

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