Add static method to enum without namespace in TypeScript

enumUtil.ts

type NoConflict<
  A extends Record<string | symbol, unknown>,
  B extends string | number | symbol
> = { [K in keyof A]: K extends B ? never : A[K] };

type PropsUnion<A> = { [K in keyof A]: A[K] }[keyof A];

export function withMethods<
  Origin extends Record<string | symbol, unknown>,
  Methods extends Record<string | symbol, unknown>
>(
  origin: NoConflict<Origin, 'T'>,
  methods: NoConflict<Methods, keyof Origin | 'T'>
): NoConflict<Origin, 'T'> &
  NoConflict<Methods, keyof Origin | 'T'> & { T: PropsUnion<Origin> } {
  return { ...origin, ...methods, T: (null as unknown) as PropsUnion<Origin> };
}

Enum with Static Method

You can add a static method to TypeScript's enum without losing type safety(but some changes) & autocompleting.

Example