Typescript: instance of an abstract class

4021 views typescript
2

Ok. this is very simple, just to remove an annoying error message.

I have an abstract class Router:

export abstract class Router {
}

And an interface like this

interface IModule {
    name: string;
    forms: Array<IForm>,
    route: typeof Router
}

Now I have a class which looks like this, and many others based on Router abstract

export class Module1 extends Router {
}

Now, I want to instantiate the route like this:

let module: IModule = { 
    name: "My Module",
    forms: [],
    route: Module1
}

let router = new module.route(); 
// TS2511: Cannot create an instance of an abstract class.

The code run just fine, and the instance of router = new Module1() is made properly, but I obviously doesn't write it properly in Typescript because I see TS2511: Cannot create an instance of an abstract class. when transpiling.

What is the correct way to define this?

Thank you

answered question

are you sure Module1 implements all the abstract method defined in Router??

1 Answer

7

When you have an abstract class, it's constructor is only invokable from a derived class, since the class is abstract and should not be instantiated. This carries over when you type something as typeof AbstractClass, the constructor will not be callable.

The solution would to be to not use typeof Router nut rather a constructor signature that returns a Router

interface IModule {
    name: string;
    forms: Array<IForm>,
    route: new () => Router
}

Another solution if you need to access static methods of Router is to create an interface derived from typeof Router which will erase the abstractness of the constructor:

export abstract class Router {
    static m(): void { console.log("Router"); }
}
type RouterClass = typeof Router;
interface RouterDerived extends RouterClass { }

interface IModule {
    name: string;
    route: RouterDerived
}

export class Module1 extends Router {
    static m(): void { console.log("Module1"); }
}

let module: IModule = { 
    name: "My Module",
    route: Module1
}

module.route.m();
let router = new module.route(); 

posted this

Have an answer?

JD

Please login first before posting an answer.