uniq.ts

const uniq = <T>(arr: T[], fn: (el: T) => Object = (a) => a) =>
  arr.reduce<T[]>(
    (acc, curr) => (acc.some((a) => fn(a) === fn(curr)) ? acc : [...acc, curr]),
    [],
  );

test("uniq", () => {
  const deduped = uniq([{ a: 2 }, { a: -2 }], (el) => Math.abs(el.a));
  expect(deduped).toEqual([{ a: 2 }]);
});