How to implement a factory method in typescript?

Question

My code:

class Model {}

class Loader {
    static load<M extends Model>(ModelClass: typeof Model): M {
        return new ModelClass();
    }
}

Error message: Type 'Model' is not assignable to type 'M'.

Link to Playground: goo.gl/qrSsoX

score 1 · Answer 1 · answered Sep 05 '18 at 10:54

1

We should say that load take a class as argument not an instance.

export interface Type<T> extends Function { new (...args: any[]): T; }

class Model {}

class Loader {
    static load<M extends Model>(ModelClass: Type<M>): M {
        return new ModelClass();
    }
}

for more information take a look at this answer

answered Sep 05 '18 at 10:54

Buggy

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And how can this problem be solved? Plz see: goo.gl/DqEeBs – Khusamov Sukhrob Sep 05 '18 at 11:47
Is that right? `static load(ModelClass: Type & typeof Model): M {...` – Khusamov Sukhrob Sep 05 '18 at 12:34
I guess so, TypeScript have [problem](https://github.com/Microsoft/TypeScript/issues/14600) with `static` methods. – Buggy Sep 05 '18 at 12:55
Since `Type` is an interface for the static side of the class (i.e., the constructor function), not the instance, you can declare `m1` directly as a method of `Type` without the `static` modifier. – Matt McCutchen Sep 05 '18 at 14:06
Sure, if you are happy with intersecting with `typeof Model`, that is a fine solution. – Matt McCutchen Sep 05 '18 at 15:12

How to implement a factory method in typescript?

1 Answers1