Get a union type derived from values of a const asserted array

ArrayValues.ts

/**
 * Get a union type derived from values of a const asserted array.
 * @example
 * const values = ['foo', 'bar'] as const;
 * type Val = ArrayValues<typeof values>;
 * // => 'foo' | 'bar'
 *
 * See https://github.com/microsoft/TypeScript/issues/28046#issuecomment-607145719
 */
export type ArrayValues<T extends ReadonlyArray<unknown>> = T[number];
  

Previous version:

// See https://github.com/microsoft/TypeScript/issues/28046#issuecomment-480516434
export type ArrayValues<T extends ReadonlyArray<unknown>> = T extends ReadonlyArray<infer ElType>
  ? ElType
  : never;