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Countdown Timer Kit in JavaScript, Free with Live Demo

Free countdown timer kit in plain JavaScript. Event countdown to any date and time zone, a daily sale timer, a kitchen timer with an alarm sound and a stopwatch with laps. Accurate even in background tabs.

Open live demo Download HTML file View code on GitHub

Countdown Timer Kit JavaScript project: an event countdown, a sale timer, a kitchen timer with sound and a stopwatch with laps

Runs on: performance.now and the Web Audio API. Works in all modern browsers. Sound needs one tap on Start first, which all browsers require.

What is the Countdown Timer Kit?

Four timers in one kit. An event countdown to any date in any time zone, a daily sale timer that ends at midnight local time, a kitchen timer with a progress ring and alarm, and a stopwatch with laps.

All of them count from real clock times rather than adding up ticks, so they stay accurate after the tab has been hidden or the phone has been locked.

Good for

Launch and event pages
Sales and offers
Cooking, workouts and study sessions
Games and quizzes

What this project does

Event countdown with time zone choice
Honest daily sale timer
Kitchen timer with ring, sound and vibration
Stopwatch with best and worst laps
Accurate in background tabs

How it works

Count to a target timeTimers store the end time, not a counter. Each tick works out what is left from the clock, so background tabs and slow devices never drift.
Time zones done rightThe event countdown converts the chosen date and zone into an exact moment, so everyone sees the same countdown wherever they are.
Sound without filesThe kitchen timer makes three beeps with the Web Audio API. The audio context starts on the Start click, which browsers require.

The key JavaScript

This is the heart of the project. The full file has the rest, including the screen layout and error handling.

let end = performance.now() + minutes * 60000;
function tick() {
  const left = Math.max(0, end - performance.now());   // no drift
  display.textContent = format(left);
  if (left === 0) beep(); else requestAnimationFrame(tick);
}
function beep() {
  const ctx = new AudioContext(), osc = ctx.createOscillator();
  osc.frequency.value = 880; osc.connect(ctx.destination);
  osc.start(); osc.stop(ctx.currentTime + 0.3);
}

How to use it

Click Download HTML file above.
Open the file in a code editor, like VS Code.
Run it from a local server with npx serve . so the camera, microphone and AI features are allowed.
Change the text and colors, then upload it to GitHub Pages, Netlify or your own site. It is one file with no build step.