How to declare an interface with static method?

Question

I want to declare an alternative constructor in interface - baz in IFoo, but seems like it's impossible in TypeScript:

interface IFoo {
    bar(): boolean;
    static baz(value): IFoo; 
}

class Foo implements IFoo {
    constructor(private qux) {}
    bar(): boolean {
        return this.qux; 
    }
    static baz(value): IFoo {
        return new Foo(value);
    }
}

What is the way to do that and have a proper type checking for baz?

Answer 1

you can do this with anonymous classes:

In general

export const MyClass: StaticInterface = class implements InstanceInterface {
}

Your example:

interface IFooStatic {
  baz(value): IFoo;
}

interface IFoo {
  bar(): boolean;
}

const Foo: IFooStatic = class implements IFoo {
  constructor(private qux) {}
  bar(): boolean {
    return this.qux; 
  }
  static baz(value): IFoo {
    return new Foo(value);
  }
}