TypeScript: typings based on object keys that come from enum

Question

I have an enum. I'd like to use its values to create typings for an object where these values became keys. The following example demonstrates what I'd like to achieve:

export enum MyEnum {
  PROP_1 = "prop 1",
  PROP_2 = "prop 2",
  // ... more props
}

export interface MyInterface {
  property: {
    "prop 1": boolean,
    "prop 2": boolean,
    // ... more props
  }
}

It works fine, but I'd like to avoid repeating all the properties from enum in the interface.

Is it possible to do something like:

export enum MyEnum {
  PROP_1 = "prop 1",
  PROP_2 = "prop 2",
  // ... more props
}

// PSEUDOCODE!
export interface MyInterface {
  property: {
    [values from MyEnum]: boolean
  }
}

---

UPDATE:

Thanks @jcalz for the solution:

enum MyEnum {
  PROP_1 = "prop 1",
  PROP_2 = "prop 2",
  // ... more props
}

interface PropertyInterface extends Record<MyEnum, boolean> {}

interface MyInterface {
  property: PropertyInterface,
}

It works good, according to what I wrote before, but I've just realized that I forgot to mention that I need all these properties to be optional.

The given solution works if a variable that implements MyInterface is defined as follows:

// VALID!
const myVariable: MyInterface = {
  property: {
    "prop 1": true,
    "prop 2": true,
  },
};

But does not work if I omit some keys as follows:

// INVALID :(
const myVariable: MyInterface = {
  property: {
    "prop 1": true,
  },
};

Answer 1

Support for this was added in TypeScript 2.9 as part of expanded key support mapped types. Specifically:

A mapped type { [P in K]: XXX } permits any K assignable to string | number | symbol.

That means you can make a type alias to a mapped type with enum values as the key:

enum MyEnum {
  PROP_1 = "prop 1",
  PROP_2 = "prop 2",
  // ... more props
}

type MyEnumValuedKeys = { [K in MyEnum]: boolean; }
// identical to 
// type MyEnumValuedKeys = {
//  "prop 1": boolean;
//  "prop 2": boolean;
//  ... more props
// }

You can make mapped type properties optional by adding a ? after the index-like key:

type OptionalMyEnumValuedKeys = { [K in MyEnum]?: boolean; }
// identical to 
// type MyEnumValuedKeys = {
//  "prop 1"?: boolean;
//  "prop 2"?: boolean;
//  ... more props
// }

So you can use OptionalMyEnumValuedKeys as your PropertyInterface. It is a type alias and not an interface. That usually doesn't matter but in case it does, TypeScript 2.8 introduced the abilitity to extend certain concrete mapped types, so you can get an interface like this:

type OptionalMyEnumValuedKeys = { [K in MyEnum]?: boolean; };
interface PropertyInterface extends OptionalMyEnumValuedKeys {} // add no properties

This could also be accomplished by using the built-in Record and Partial type aliases:

interface PropertyInterface extends Partial<Record<MyEnum, boolean>> {}

Okay, hope that helps. Good luck!