@arki/clock

Clock abstraction for testable time-dependent code, with deterministic mock and system implementations.

Installation

npm install @arki/clock
# or
bun add @arki/clock
# or
pnpm add @arki/clock

Why

Code that calls new Date() or Date.now() directly is hard to test deterministically. Inject a Clock instead, and tests can swap in MockClock to advance time on demand — useful for cooling windows, scheduled jobs, expiration logic, and any time-sensitive flow.

Usage

Production code

import { SystemClock, type Clock } from '@arki/clock';
 
function makeService(clock: Clock = new SystemClock()) {
  return {
    isExpired(at: Date) {
      return clock.now().getTime() > at.getTime();
    },
  };
}

Tests

import { MockClock } from '@arki/clock';
import { describe, expect, it } from 'vitest';
 
describe('isExpired', () => {
  it('returns true after the deadline passes', () => {
    const clock = new MockClock(new Date('2026-01-01T00:00:00.000Z'));
    const service = makeService(clock);
    const deadline = new Date('2026-01-01T01:00:00.000Z');
 
    expect(service.isExpired(deadline)).toBe(false);
 
    clock.advance(60 * 60 * 1000 + 1);
    expect(service.isExpired(deadline)).toBe(true);
  });
});

API

Clock

Interface with a single method:

• now(): Date — return the current time as a Date.

SystemClock

Production implementation backed by the runtime Date. now() returns new Date().

MockClock

Controllable clock for tests.

• new MockClock(initialNow?: Date) — defaults to the Unix epoch.
• now(): Date — returns a fresh Date on every call (callers cannot corrupt internal state by mutating it).
• advance(ms: number): void — moves time forward. Throws RangeError on negative or non-finite values.
• setNow(date: Date): void — sets absolute time; allowed to go backward for arranging past scenarios.

Documentation

@arki/clock is framework-agnostic and works on its own. When you compose it with the @arki/dot application framework, see packages/dot/docs/ for plugin authoring, lifecycle, and diagnostics.

License

MIT. See LICENSE.