TypeScript generics create instace

Question

I'm trying to create a factory for instantiating my classes with generics. Checked out TypeScript docs and it all works perfectly. In short, this works just fine:

class Person {
    firstName = 'John';
    lastName = 'Doe';
}

class Factory {
    create<T>(type: (new () => T)): T {
        return new type();
    }
}

let factory = new Factory();
let person = factory.create(Person);

console.log(JSON.stringify(person));

Now define class Person in directory:

export class Person extends BasePerson {
    firstName = 'John';
    lastName = 'Doe';
}

And when I import Person from other package:

import { Person } from "./directory"

class Factory {
    create<T>(type: (new () => T)): T {
        return new type();
    }
}

let factory = new Factory();
let person = factory.create(Person);

I get error: Argument of type 'typeof Person' is not assignable to parameter of type 'new () => Person'

How can I get a value of Person instead of typeof Person?

Using TypeScript 3.7.2 and Node v10.13.0.

Inch High · Accepted Answer · 2019-12-10 15:43:50Z

1

Could you try this for me please?

import { Person } from "./directory"

class Factory {
    create<T>(type: (new () => T)): T {
        return new type();
    }
}

let factory = new Factory();
let person = factory.create(new Person);

answered Dec 10, 2019 at 15:43

Inch High

8455 silver badges17 bronze badges

Sign up to request clarification or add additional context in comments.

5 Comments

pavle Over a year ago

thumbs up for the quick answer :) it is not a valid statement though, but I solved it. It is a little embarrasing, i had a parent class that expected an argument in its contructor, removed it and now everything works perfectly!

messerbill Over a year ago

@pavle could you please add an answer how you solved your problem or - if this is really the correct answer - mark it with the green hook?

Inch High Over a year ago

Your welcome @pavle, as mentioned by messerbill it might be a good idea to post your solution for any future folk who are experiencing a similar issue.

pavle Over a year ago

@InchHigh done. Inheritance was the problem, but with better dependency composition, problem was solved. Composition over inheritance!

Inch High Over a year ago

Good stuff :) - Glad you sorted it.

pavle · Accepted Answer · 2019-12-11 09:02:21Z

0

Actual problem here was a parent class of Person -> BasePerson. BasePerson expected an argument in its constructor, so when I tried to call factory.create(Person), Person actually was an typeof because it expected an argument for base class constructor. Problem was solved by deleting the constructor in base class and injecting a property via ioc container, in my case Inversify.

answered Dec 11, 2019 at 9:02

pavle

93916 silver badges40 bronze badges

Collectives™ on Stack Overflow

TypeScript generics create instace

2 Answers 2

5 Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

5 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related