Home > types > RequireExactlyOne
Create a type that requires exactly one of the given keys and disallows more. The remaining keys are kept as is.
Use-cases: - Creating interfaces for components that only need one of the keys to display properly. - Declaring generic keys in a single place for a single use-case that gets narrowed down via RequireExactlyOne.
The caveat with RequireExactlyOne is that TypeScript doesn’t always know at compile time every key that will exist at runtime. Therefore RequireExactlyOne can’t do anything to prevent extra keys it doesn’t know about.
Signature:
export declare type RequireExactlyOne<ObjectType, KeysType extends keyof ObjectType = keyof ObjectType> =
{[Key in KeysType]: (
Required<Pick<ObjectType, Key>> &
Partial<Record<Exclude<KeysType, Key>, never>>
)}[KeysType] & Omit<ObjectType, KeysType>;
``` import {RequireExactlyOne} from ‘type-fest’;
type Responder = { text: () => string; json: () => string; secure: boolean; };
const responder: RequireExactlyOne<Responder, ‘text’ | ‘json’> = { // Adding a text key here would cause a compile error.
json: () => ‘{“message”: “ok”}’, secure: true }; ```
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