groupByProp.ts

const groupByProp = <P extends string, O extends { [Key in P]: string }>(
  objects: O[],
  prop: P,
) => {
  return objects.reduce((groups, object) => {
    const key = object[prop];
    return { ...groups, [key]: (groups[key] ?? []).concat(object) };
  }, {} as Record<O[P], O[]>);
};