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

Buggy · Accepted Answer · 2018-09-05 10:54:31Z

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 5, 2018 at 10:54

Buggy

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5 Comments

Khusamov Sukhrob Over a year ago

And how can this problem be solved? Plz see: goo.gl/DqEeBs

Khusamov Sukhrob Over a year ago

Is that right? static load<M extends Model>(ModelClass: Type<M> & typeof Model): M {...

Buggy Over a year ago

I guess so, TypeScript have problem with static methods.

Matt McCutchen Over a year ago

Since Type<T> 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<T> without the static modifier.

Matt McCutchen Over a year ago

Sure, if you are happy with intersecting with typeof Model, that is a fine solution.

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