How specify class definition as parameter type in Typescript

Question

I would like to pass type information for class, with hinting the compiler that the given parameter is not an instance of a class but the class definition. How can I do that?

import * as Routes from '../routes';
import * as Entities from '../entities';

export class RouteManager {
  public router = Router();
  private connection = getConnectionManager().get();

  constructor() {
    this.addRoute(Routes.VideoRoute, Entities.Video);
  }

  addRoute(routeClass: AbstractRoute<AbstractEntity>, entity: AbstractEntity): void {
    const instance = new routeClass(entity, this.connection.getRepository(entity))
    this.router.get(instance.route, instance.find);
  }
}

Here the compiler complains about the new routeClass(entity, this.connection.getRepository(entity)) line because it thinks routeClass is an instance of AbstractRoute<AbstractEntity> and not the exported class definition for it.

I have tried usingAbstractRoute<AbstractEntity>.constructor but Typescript doesn't seem to know this structure.

You linked to this question o.O

Sebastian Sebald
– Sebastian Sebald

2017-04-25 09:48:41 +00:00
Commented Apr 25, 2017 at 9:48 — Sebastian Sebald
– Sebastian Sebald, Commented Apr 25, 2017 at 9:48
sorry! :D stackoverflow.com/questions/34698710/…

Thiago Barcala
– Thiago Barcala

2017-04-25 10:00:04 +00:00
Commented Apr 25, 2017 at 10:00 — Thiago Barcala
– Thiago Barcala, Commented Apr 25, 2017 at 10:00

Sebastian Sebald · Accepted Answer · 2017-04-25 09:50:56Z

12

The syntax for this looks a little bit weird. Basically you define a signature that uses something like new(...args: any[]) => T. You of course can be more strict by replacing T with your class and the args with the constructor signature.

I would recommend something like this:

class Foo {}
type Constructor<T> = new(...args: any[]) => T;

function createFoo(thing: Constructor<Foo>) { return new thing(); }

answered Apr 25, 2017 at 9:50

Sebastian Sebald

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4 Comments

NoNameProvided Over a year ago

It throws the following: Type 'typeof Video' is not assignable to type 'Constructor<Video>'. Type 'Video' is not assignable to type 'Video'. Two different types with this name exist, but they are unrelated.

Sebastian Sebald Over a year ago

There is no Video type in your example, but from the looks of it you're using the same identifier multiple times. That's also what the error tells you: Two different types with this name exist PS: This seems to be an issue with your code. Can you copy/paste my example code into your code base + check if it works?

J-Cake Over a year ago

okay hear me out: what if I want to say that I can accept any class so long as it extends class Bar?

Sebastian Sebald Over a year ago

You mean polymorphism?

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