An index signature parameter type cannot be a union type. Consider using a mapped object type instead

Question

You can use TS "in" operator and do this:

enum Options {
  ONE = 'one',
  TWO = 'two',
  THREE = 'three',
}
interface OptionRequirement {
  someBool: boolean;
  someString: string;
}
type OptionRequirements = {
  [key in Options]: OptionRequirement; // Note that "key in".
}

The simplest solution is to use Record

type OptionRequirements = Record<Options, OptionRequirement>

You can also implement it yourself as:

type OptionRequirements = {
  [key in Options]: OptionRequirement;
}

This construct is only available to type, but not interface.

The problem in your definition is saying the key of your interface should be of type Options, where Options is an enum, not a string, number, or symbol.

The key in Options means "for those specific keys that's in the union type Options".

type alias is more flexible and powerful than interface.

If your type does not need to be used in class, choose type over interface.

I had some similar problem but my case was with another field property in interface so my solution as an example with optional field property with an enum for keys:

export enum ACTION_INSTANCE_KEY {
  cat = 'cat',
  dog = 'dog',
  cow = 'cow',
  book = 'book'
}

type ActionInstances = {
  [key in ACTION_INSTANCE_KEY]?: number; // cat id/dog id/cow id/ etc // <== optional
};

export interface EventAnalyticsAction extends ActionInstances { // <== need to be extended
  marker: EVENT_ANALYTIC_ACTION_TYPE; // <== if you wanna add another field to interface
}

In my case:

export type PossibleKeysType =
  | 'userAgreement'
  | 'privacy'
  | 'people';

interface ProviderProps {
  children: React.ReactNode;
  items: {
    //   ↙ this colon was issue
    [key: PossibleKeysType]: Array<SectionItemsType>;
  };
}

I fixed it by using in operator instead of using :

~~~

interface ProviderProps {
  children: React.ReactNode;
  items: {
    //     ↙ use "in" operator
    [key in PossibleKeysType]: Array<SectionItemsType>;
  };
}

Instead of using an interface, use a mapped object type

enum Option {
  ONE = 'one',
  TWO = 'two',
  THREE = 'three'
}

type OptionKeys = keyof typeof Option;

interface OptionRequirement {
  someBool: boolean;
  someString: string;
}

type OptionRequirements = {                 // note type, not interface
  [key in OptionKeys]: OptionRequirement;   // key in
}

In my case I needed the properties to be optional, so I created this generic type.

type PartialRecord<K extends string | number | symbol, T> = { [P in K]?: T; };

Then use it as such:

type MyTypes = 'TYPE_A' | 'TYPE_B' | 'TYPE_C';

interface IContent {
    name: string;
    age: number;
}

interface IExample {
    type: string;
    partials: PartialRecord<MyTypes, IContent>;
}

Example

const example : IExample = {
    type: 'some-type',
    partials: {
        TYPE_A : {
            name: 'name',
            age: 30
        },
        TYPE_C : {
            name: 'another name',
            age: 50
        }
    }
}