createEnum(): helper for creating enum objects

create-enum.ts

// More information on enum objects as an alternative to enums:
// https://2ality.com/2025/01/typescript-enum-patterns.html#alternative-to-enum%3A-object-literal-1

/**
 * Returns an enum object. Adds the following improvements:
 * - Sets the prototype to `null`.
 * - Freezes the object.
 * - The result has the same type as if `as const` had been applied.
 */
function createEnum<
  // The two type variables are necessary so that the result has specific
  // property value types.
  T extends { [idx: string]: V },
  V extends
    | undefined | null | boolean | number | bigint | string | symbol 
    | object
>(enumObj: T): Readonly<T> {
  // Copying `enumObj` produces “faster” objects than Object.setPrototypeOf()
  return Object.freeze({
    __proto__: null,
    ...enumObj,
  });
}

const Tree = createEnum({
  Maple: 'Maple',
  Oak: 'Oak',
});

type X = typeof Tree;
// {
//   readonly Maple: "Maple";
//   readonly Oak: "Oak";
// }