Using enum as interface key in typescript

I was wonder if I can use enum as an object key in interfaces.. I've built a little test for it:

export enum colorsEnum{
red,blue,green
}

export interface colorsInterface{
[colorsEnum.red]:boolean,
[colorsEnum.blue]:boolean,
[colorsEnum.green]:boolean
}

When I run it I'm getting the following error:

A computed property name in an interface must directly refer to a built-in symbol.

I'm doing it wrong or it just not possible?

You can try with type:

export enum colorsEnum{
    red, blue, green
}

export type colorsInterface = {
    [key in colorsEnum]: boolean;
};

let example: colorsInterface = {
    [colorsEnum.red]: true,
    [colorsEnum.blue]: false,
    [colorsEnum.green]: true
};

Or if you do not want to use all keys: add a ?

export type colorsInterface = {
    [key in colorsEnum]?: boolean;
};

let example: colorsInterface = {
    [colorsEnum.red]: true,
    [colorsEnum.blue]: false
};

OK, the key idea is to convert the Enum to the correct Type and to extends the Interface with it: You can check it out in live code here.

const enum Enum {
    key1 = "value1",
    key2 = "value2",
    key3 = "value3",
}
type EnumKeys = keyof typeof Enum;
type EnumKeyFields = {[key in EnumKeys]:boolean}

interface IEnumExtended extends EnumKeyFields {
    KeyEx1:boolean;
    KeyEx2:string;
}

// Test it
const enumInstance: IEnumExtended = {
    
};

when you inside the enumInstance you will get autocomplete for the Enum keys and not the values.

To define an interface, the member names must be supplied not computed.

export interface colorsInterface {
    red: boolean;
    blue: boolean;
    green: boolean;
}

If you are worried about keeping the enum and the interface in sync you could use the following:

export interface colorsInterface {
    [color: number]: boolean;
}

var example: colorsInterface = {};
example[colorsEnum.red] = true;
example[colorsEnum.blue] = false;
example[colorsEnum.green] = true;

TypeScript is perfectly happy for you to pass the enum as the index and a rename-refactor would then keep everything together if you decided to rename red, for example.

A simple solution using the native Record<Keys, Type> utility. (Docs)

export enum Colors {
    RED = 'red',
    GREEN = 'green',
    BLUE = 'blue'
}

export type ColorInterface = Record<Colors, boolean>

This type translates to:

// translates to:

export type ColorInterface = {
    red: boolean;
    green: boolean;
    blue: boolean;
}

---

IMPORTANT: You must to define an enum key and map the values accordingly to them, else, you'll get a type / interface that uses an enum's index like the following:

export enum Colors {
    'red',
    'green',
    'blue'
}

export type ColorInterface = Record<Colors, boolean>

// translates to:

export type ColorInterface = {
    0: boolean;
    1: boolean;
    2: boolean;
}

Alternatively, you can also define the Colors using type alias if you don't want to explicitly define the enum keys or if you have just a few keys to use, this will also translate properly to what you need:

export type Colors = 'red' | 'green' | 'blue'

// will also translate to:

export type ColorInterface = {
    red: boolean;
    green: boolean;
    blue: boolean;
}

This worked for us:

type DictionaryFromEnum = {
  [key in keyof typeof SomeEnum]?: string
}

Why not to keep it as simple as it should be:

export enum Color {
    Red = 'red',
    Blue = 'blue',
    Green = 'green'
}

export interface IColors{
    [Color.Red]: boolean,
    [Color.Blue]: boolean,
    [Color.Green]: boolean
}

Probably you are searching for key remapping via as.

> Note: Requires TypeScript ^4.1.

Example:

enum Color {
  red,
  blue,
  green,
}

// Define valid colors
// type TColor = 'red' | 'blue' | 'green';
type TColor = keyof typeof Color;

// Define object structure, with `color` as prefix for each `TColor`
type TWithColorCode = {
  [colorKey in TColor as `color${Capitalize<string & colorKey>}`]: string;
};

const a: TWithColorCode = {
  // All properties will be required
  colorGreen: '#00FF00',
  colorBlue: '#0000FF',
  colorRed: '#FF0000',
};

// Extending an `interface`:

export interface ICarRGB extends TWithColorCode {
  id: number;
  name: string;
  // Optional property
  createdAt?: Date;
}

const b: ICarRGB = {
  id: 1,
  name: 'Foo',
  colorGreen: '#00FF00',
  colorBlue: '#0000FF',
  colorRed: '#FF0000',
};