export const partition = <T>(
  arr: readonly T[],
  predicate: (item: T) => boolean,
): [T[], T[]] => {
  const truthy: T[] = [];
  const falsy: T[] = [];
  for (const item of arr) {
    (predicate(item) ? truthy : falsy).push(item);
  }
  return [truthy, falsy];
};

// Usage
const [evens, odds] = partition([1, 2, 3, 4, 5], n => n % 2 === 0);
// evens: [2, 4]
// odds: [1, 3, 5]