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.

Try putting Normal in "Normal"

Simon H
– Simon H

2016-02-09 17:35:04 +00:00
Commented Feb 9, 2016 at 17:35 — Simon H
– Simon H, Commented Feb 9, 2016 at 17:35

zlumer · Accepted Answer · 2016-02-09 17:41:23Z

2

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 (e.g. 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.

answered Feb 9, 2016 at 17:41

zlumer

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3 Comments

micah Over a year ago

Guess I can't have my cake and eat it too. Thanks!

zlumer Over a year ago

Actually, the 2nd option is pretty good in terms of type safety. What is your main reason to declare IMyEnum?

micah Over a year ago

Trying to add some sense to some old code I've adopted. I would have liked to have each object bound by the same rules through the compiler than loosely abiding to them in convention. But this is good enough.

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