Property Doesn't Exist on Typescript Interface

Question

I have a custom "Enum" interface that that has a value and a description. I've defined an my enum interface like this-

module App {
  export interface IMyEnum {
    [index: string]: IMyEnumValue;
  }

  export interface IMyEnumValue {
      value: any;
      text: string;
  }
}

And my enums like this-

/// <reference path="./enums.interface.ts"/>

module App {
  export const StatusEnum: IMyEnum = {
    Normal: { value: 100, text: 'Normal' },
    Overdue: { value: 200, text: 'Overdue' },
    Critical: { value: 300, text: 'Critical' }
  }
}

But the typescript compiler is complaining that "Normal" does not exist on type IMyEnum.

let statusCode = StatusEnum.Normal.value;

Is there anyway to do this without defining an IStatusEnum interface? I think that would be over-engineering.

Answer 1

When you cast StatusEnum to IMyEnum , you actually lose type info, leaving you only with an indexer: [index: string]: IMyEnumValue

Option 1: use strings

let statusCode = StatusEnum["Normal"].value;

You'll lose compile-time safety on enum names (eg StatusEnum["normal"].value will give a runtime error).

Option 2: get rid of IMyEnum and let the compiler infer the type.

  export const StatusEnum = {
    Normal: { value: 100, text: 'Normal' },
    Overdue: { value: 200, text: 'Overdue' },
    Critical: { value: 300, text: 'Critical' }
  }

let statusCode = StatusEnum.Normal.value;

That way you'll have type safety and autocompletion.