endOfDay

1/**
2 * Returns a new Date object set to the end of the given day (23:59:59.999).
3 *
4 * @param date - The input date.
5 * @returns A new Date representing the end of the day.
6 */
7export function endOfDay(date: Date): Date {
8  return new Date(date.getFullYear(), date.getMonth(), date.getDate(), 23, 59, 59, 999);
9}

• Precise Daily Upper Bound

  Sets the time to 23:59:59.999, which is the exact last millisecond of the day — ideal for inclusive range comparisons.

• Immutable

  Returns a new Date instance, preserving the integrity of the input.

• Consistent Local Time Behavior

  Works in the system's local timezone, aligning with how most user-facing apps handle dates.

• Minimal & Efficient

  Uses direct construction — no need for cloning or incremental time adjustments.

Tests | Examples

1test('endOfDay - sets time to 23:59:59.999', () => {
2  const input = new Date('2023-08-25T10:00:00.000Z');
3  const result = endOfDay(input);
4
5  expect(result.getFullYear()).toBe(2023);
6  expect(result.getMonth()).toBe(7); // August
7  expect(result.getDate()).toBe(25);
8  expect(result.getHours()).toBe(23);
9  expect(result.getMinutes()).toBe(59);
10  expect(result.getSeconds()).toBe(59);
11  expect(result.getMilliseconds()).toBe(999);
12});
13
14test('endOfDay - does not mutate original date', () => {
15  const input = new Date('2023-08-25T00:00:00.000Z');
16  const copy = new Date(input.getTime());
17  endOfDay(input);
18  expect(input).toEqual(copy);
19});

Common Use Cases

• Date Range Filters

  Define inclusive end boundaries in search or report queries (e.g., filter all events through the end of a specific day).

• Batch Processing Windows

  Schedule tasks or run analytics through the end of each day without missing late entries.

• Calendar UI Boundaries

  Highlight or block out full-day selections including the last moment of a day.

• Validation Logic

  Ensure a timestamp does not exceed the end of a day for business rules or user input validation.

• Backup & Archival Systems

  Tag or finalize daily datasets with an end-of-day marker.