Pomodoro timer

The point of this package is that a running timer carries no seconds. While running, the state holds endsAt — a wall-clock epoch ms — and the client draws the countdown from it. So the clock below ticks every second, but state only changes when you press something or when a phase actually expires.

What to try

• Press start, then start again. The second one returns null — reduce treats an already-running timer as a no-op rather than throwing or restarting.
• Press pause and watch endsAt become null while remaining freezes at whatever was left.
• Press skip a few times. The phase alternates, but cycles stays put — only a phase that expires on its own counts as a completed cycle.
• Set work to 0 and send it. It clamps to 1 minute rather than falling back to the current config, because 0 is a value that converts to a number. Try 999 too: it clamps to 120.
• Try configure while the timer is running. It returns null — changing a phase length mid-phase has ambiguous semantics, so only a stopped timer accepts it.

The code behind it

The demo imports the published package and nothing else:

import { defaultState, onTimer, reduce, timerDelay } from '@insession/extension-pomodoro';

let state = defaultState();

// A button press
const next = reduce(state, 'start');
if (next) state = next;

// Phase transitions are driven by your own timer
const delay = timerDelay(state); // ms until the phase ends, or null
if (delay !== null) setTimeout(() => { state = onTimer(state); }, delay);

reduce is a pure function — no I/O, no timers started inside it. Scheduling is yours, which is what lets the same state machine run on a server, in a test, or in this page.

See the package reference for the full action list and the persistence helpers (restore / persistState).