Browser Support

Chrome 4+ · Firefox 4+ · Safari 4+ · Edge 12+

Create Connection

WebSocket constructor takes two arguments:

const ws = new WebSocket(url, [protocols]);

Parameter	Type	Description
url	string	WebSocket server address, must be ws:// or wss://
protocols	string | string[]	Optional, subprotocol name

Lifecycle Events

WebSocket has four core events:

const ws = new WebSocket('wss://echo.websocket.org');

ws.onopen = () => {
  // Handshake successful, connection established, can send messages now
};

ws.onmessage = (event) => {
  const data = event.data;
  console.log('Received:', data);
};

ws.onerror = (event) => {
  console.error('WebSocket error');
};

ws.onclose = (event) => {
  console.log('Close code:', event.code);
  console.log('Reason:', event.reason);
};

readyState

Value	Constant	Meaning
0	CONNECTING	Connecting
1	OPEN	Connected, can send messages
2	CLOSING	Closing
3	CLOSED	Closed

Send Messages

ws.send('Hello');
ws.send(JSON.stringify({ type: 'message', content: 'Hello' }));

const buffer = new ArrayBuffer(8);
const view = new DataView(buffer);
view.setFloat32(0, 3.14);
ws.send(buffer);

Close Connection

ws.close(1000, 'Done');

Notes

• Sending large messages: WebSocket has no hard limit on single message size, but messages >1MB should be sent in chunks
• UTF-8 encoding: Strings are encoded as UTF-8 by default; don't send binary data as strings (triggers encoding conversion)
• Browser doesn't auto-reconnect: If you need to recover after close, you must manually new WebSocket() again