0Pricing
WebSockets & Realtime Systems Programming · Lesson

Automatic Reconnection on the Client

Build a resilient browser WebSocket client that detects drops and reconnects automatically with exponential backoff and message queuing.

Automatic Reconnection on the Client is a free WebSockets & Realtime Systems Programming lesson on CoddyKit — lesson 4 of 4. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the WebSockets & Realtime Systems Programming learning path, one of 4 lessons in the course, and your progress syncs across the web and the CoddyKit app.

Connections Drop

Networks are unreliable. Wi-Fi hiccups, tabs sleep, and servers restart. A good client detects a closed socket and reconnects without the user noticing.

Detecting a Drop

The browser fires close when the connection ends and error on failures. Reconnection logic hooks into close.

ws.addEventListener('close', () => {
  scheduleReconnect();
});

Naive Reconnect Is Risky

Reconnecting instantly in a tight loop can hammer a struggling server. Instead, wait longer after each failed attempt.

Exponential Backoff

Double the delay each attempt, up to a cap, so a recovering server is not overwhelmed.

let attempt = 0;
function delay() {
  return Math.min(1000 * 2 ** attempt, 30000);
}

Adding Jitter

If many clients reconnect at once, they create a thundering herd. Random jitter spreads them out.

function delayWithJitter() {
  return delay() * (0.5 + Math.random() * 0.5);
}

The Reconnect Function

Wrap connection creation so each attempt re-binds handlers and schedules the next retry on failure.

function connect() {
  ws = new WebSocket(url);
  ws.addEventListener('open', onOpen);
  ws.addEventListener('close', scheduleReconnect);
}

Resetting on Success

When a connection opens successfully, reset the attempt counter so future drops start backoff fresh.

function onOpen() {
  attempt = 0;
  flushQueue();
}

Queuing Messages While Down

If the user sends while disconnected, buffer the message and send it once reconnected.

const queue = [];
function send(data) {
  if (ws.readyState === WebSocket.OPEN) ws.send(data);
  else queue.push(data);
}

Flushing the Queue

On reconnect, drain the buffer in order.

function flushQueue() {
  while (queue.length) ws.send(queue.shift());
}

Giving Up Gracefully

After a max number of attempts, surface an error to the user rather than retrying forever.

function scheduleReconnect() {
  if (++attempt > 10) return showOffline();
  setTimeout(connect, delayWithJitter());
}

Best Practices

Build resilient clients:

  • Use exponential backoff with jitter
  • Reset state on a successful open
  • Queue outgoing messages while offline
  • Cap retries and inform the user

Quick Check

Test your reconnection knowledge.

Recap

You built an auto-reconnecting client:

  • Hook the close event to schedule retries
  • Use exponential backoff with jitter
  • Reset attempts on open
  • Queue and flush messages around outages

Your client now survives flaky networks.

Frequently asked questions

Is the “Automatic Reconnection on the Client” lesson free?

Yes — the full text of “Automatic Reconnection on the Client” is free to read here on the web, and the WebSockets & Realtime Systems Programming course includes 4 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the WebSockets & Realtime Systems Programming course, upgrade to CoddyKit PRO.

What will I learn in “Automatic Reconnection on the Client”?

Build a resilient browser WebSocket client that detects drops and reconnects automatically with exponential backoff and message queuing. You practise WebSockets & Realtime Systems Programming with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.

Do I need any experience to start WebSockets & Realtime Systems Programming?

No prior experience is required. WebSockets & Realtime Systems Programming on CoddyKit is structured for beginners through advanced learners; this is — lesson 4 of 4, so you can start here or from the beginning and move at your own pace.

How long does the “Automatic Reconnection on the Client” lesson take?

Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.

Can I write and run code in this WebSockets & Realtime Systems Programming lesson?

Yes. Every WebSockets & Realtime Systems Programming lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.

All lessons in this course

  1. Browser WebSocket API Fundamentals
  2. Sending and Receiving Data
  3. Client-Side Event Handling
  4. Automatic Reconnection on the Client
← Back to WebSockets & Realtime Systems Programming