Browser Support

Dedicated Worker: Chrome 4+ · Firefox 3.5+ · Safari 4+ · Edge 12+

SharedWorker: Chrome 4+ · Firefox 29+ · Safari 15.2+ · Edge 79+

Note: Safari's SharedWorker support came relatively late; mobile Safari 15.2+ has full support.

Overview

Dedicated Worker is exclusive to the main thread/tab that created it; it dies when that tab closes. Shared Worker can be shared across multiple pages, tabs, and Worker instances of the same origin.

How to choose? Need cross-tab shared state or resources? Use SharedWorker. Just running computation within one page? Use Dedicated Worker.

SharedWorker Quick Start

// === SharedWorker ===
const connections = new Set();

self.onconnect = (e) => {
  const port = e.ports[0];
  connections.add(port);

  port.onmessage = (e) => {
    connections.forEach(p => p.postMessage(e.data));
  };

  port.start();
};

// === main.js (any tab) ===
const worker = new SharedWorker('./shared-worker.js', 'my-shared-worker');

worker.port.onmessage = (e) => {
  console.log('Received broadcast:', e.data);
};

worker.port.start();
worker.port.postMessage('hello from tab 1');

When to Use Dedicated Worker?

• Background computation (sorting, compression, encryption)
• Audio/video codec processing
• Large data JSON parsing
• Timed polling (WebSocket heartbeat, server push streams)

When to Use SharedWorker?

• Cross-tab data sharing: e.g. user opens two tabs, one tab logs in, the other tab auto-syncs login state
• Cross-tab connection sharing: One WebSocket connection, multiple tabs share it, avoid rebuilding connections
• Counter/state broadcasting: Global event bus

Notes

• SharedWorker's name parameter is important. Same name points to same Worker instance; different names create different Workers
• Safari compatibility: If you need to support Safari below 15.2, don't use SharedWorker, or prepare a fallback (BroadcastChannel)
• BroadcastChannel is a lighter alternative: If you only need cross-tab communication without keeping long connection state, BroadcastChannel API is simpler