export const groupBy = <T, K extends PropertyKey>(
  arr: readonly T[],
  getKey: (item: T) => K,
): Record<K, T[]> =>
  arr.reduce(
    (acc, item) => {
      const key = getKey(item);
      (acc[key] ||= []).push(item);
      return acc;
    },
    {} as Record<K, T[]>,
  );

// Usage
const items = [
  { type: 'fruit', name: 'apple' },
  { type: 'vegetable', name: 'carrot' },
  { type: 'fruit', name: 'banana' },
];

groupBy(items, i => i.type);
// {
//   fruit: [{ type: 'fruit', name: 'apple' }, { type: 'fruit', name: 'banana' }],
//   vegetable: [{ type: 'vegetable', name: 'carrot' }]
// }