Use Enum values as a key in interface

Question

I am struggling to create an interface that uses values from an Enum.

enum TestEnum {
  'VAL1' = 'TEST1',
  'VAL2' = 'TEST2'
}

interface IMyInterface {
  [TestEnum[key in TestEnum]]: {
    // some code
  }
}

const objToType: IMyInterface = {
  TEST1: { / ** \ }
  TEST2: { / ** \ }
}

It throws an error

A computed property name in a type literal must refer to an expression whose type is a literal type or a 'unique symbol' type.

What's the problem here?

Benjamin Gruenbaum · Accepted Answer · 2022-01-29 08:57:20Z

1

I think the confusing bit is that [key in TestEnum] returns the "values" of the enum rather than the "keys" (if you want to iterate the keys you'd use [key in keyof TestEnum]).

This is easy to do using a type declaration rather than an interface declaration:

enum TestEnum {
  'VAL1' = 'TEST1',
  'VAL2' = 'TEST2'
}

type IMyInterface = {
  [key in TestEnum]: { /* */ }
}

const objToType: IMyInterface = {
  TEST1: { },
  TEST2: { }
}

Playground link

answered Jan 29, 2022 at 8:57

Benjamin Gruenbaum

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