TypeScript GroupBy Replacement for Lodash

groupby.test.ts

import { groupBy } from './groupby.ts';

describe('Array Utils Test', () => {
  it('should test groupBy', () => {
    const data = getGroupByData();
    const actual = groupBy(data, 'name');
    const expected = getGroupByExpected();
    expect(actual).toEqual(expected);
  })
})

function getGroupByData() {
  return [
    { id: 1, name: 'ABC', },
    { id: 2, name: 'XYZ', },
    { id: 3, name: 'ABC', },
  ]
}
function getGroupByExpected() {
  return {
    'ABC': [
      { id: 1, name: 'ABC', },
      { id: 3, name: 'ABC', },
    ],
    'XYZ': [
      { id: 2, name: 'XYZ', },
    ]
  }
}

groupby.ts

type GroupedByType<T> = {
  [prop in keyof T]: Partial<T>[];
};
type AvailableKeys<T> = keyof T & string;
export function groupBy<T>(arr: T[], prop: AvailableKeys<T>): GroupedByType<T> {
  const key: string = prop; // workaround for typescript shenanigans
  return arr.reduce((result: GroupedByType<T>, obj: T) => {
    (result[obj[key]] = result[obj[key]] || []).push(obj);
    return result;
  }, {} as GroupedByType<T>)
}