TypeScript Index Signatures with Interface Types

Question

I have an interface and a class:

interface Widget {
  widgetStuff(): void;
}

class Foo implements Widget {
  widgetStuff(): void {
  }
}

I want to track all of the Widgets in another class, and an index signature seems to be the easiest way:

class WidgetCatalog {
  private readonly mapping: { [key: string]: Widget };

  constructor() {
    this.mapping = {
      Foo // <= Error here
    }
  }
}

I'm getting this error: error TS2322: Type 'typeof Foo' is not assignable to type 'Widget'. Property 'widgetStuff' is missing in type 'typeof Foo'.

I'm not sure what Im missing here, since it seems to be a pretty straightforward implementation. Do I need to specify the value type in the index signature differently?

this.mapping.Foo will be Foo, the class constructor that makes new Widgets. It's not a Widget itself. So either mapping should hold Widget constructors, in which case it's mis-annotated, or this.mapping should be initialized to {Foo: new Foo()} or something. — jcalz
– jcalz, Commented Oct 3, 2019 at 19:34

Chad · Accepted Answer · 2019-10-03 19:50:53Z

1

@jcalz pointed me in the right direction. This version works:

interface Widget {
  widgetStuff(): void;
}

class Foo implements Widget {
  widgetStuff(): void {
  }
}

class WidgetCatalog {
  // Change to mapping of Widget constructors
  private readonly mapping: { [key: string]: new(...args) => Widget };

  constructor() {
    this.mapping = {
      Foo
    }
  }
}

answered Oct 3, 2019 at 19:50

Chad

4937 silver badges19 bronze badges

Sign up to request clarification or add additional context in comments.

Collectives™ on Stack Overflow

TypeScript Index Signatures with Interface Types

1 Answer 1

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Related