WebSocket

Baseline Widely available

This feature is well established and works across many devices and browser versions. It’s been available across browsers since July 2015.

Note: This feature is available in Web Workers.

The WebSocket object provides the API for creating and managing a WebSocket connection to a server, as well as for sending and receiving data on the connection.

To construct a WebSocket, use the WebSocket() constructor.

Constructor

WebSocket(): Returns a newly created WebSocket object.

Instance properties

WebSocket.binaryType: The binary data type used by the connection.
WebSocket.bufferedAmount Read only: The number of bytes of queued data.
WebSocket.extensions Read only: The extensions selected by the server.
WebSocket.protocol Read only: The sub-protocol selected by the server.
WebSocket.readyState Read only: The current state of the connection.
WebSocket.url Read only: The absolute URL of the WebSocket.

Instance methods

WebSocket.close(): Closes the connection.
WebSocket.send(): Enqueues data to be transmitted.

Events

Listen to these events using addEventListener() or by assigning an event listener to the oneventname property of this interface.

close: Fired when a connection with a WebSocket is closed. Also available via the onclose property
error: Fired when a connection with a WebSocket has been closed because of an error, such as when some data couldn't be sent. Also available via the onerror property.
message: Fired when data is received through a WebSocket. Also available via the onmessage property.
open: Fired when a connection with a WebSocket is opened. Also available via the onopen property.

Examples

// Create WebSocket connection.
const socket = new WebSocket("ws://localhost:8080");

// Connection opened
socket.addEventListener("open", (event) => {
  socket.send("Hello Server!");
});

// Listen for messages
socket.addEventListener("message", (event) => {
  console.log("Message from server ", event.data);
});

Specifications

Specification
WebSockets Standard # the-websocket-interface

Browser compatibility

	Desktop						Mobile
	Chrome	Edge	Firefox	Opera	Safari	Chrome Android	Firefox for Android	Opera Android	Safari on IOS	Samsung Internet	WebView Android
`WebSocket`	5	12	117–11	12.1	5	18	147–14	12.1	4.2	1.0	4.4
`WebSocket`	5	12	11 7–11 Message size limited to 16 MB (see bug 711205).	12.1	5	18	14 7–14 Message size limited to 16 MB (see bug 711205).	12.1	4.2	1.0	4.4
`binaryType`	15	12	11	12.1	6	18	14	12.1	6	1.0	4.4
`bufferedAmount`	5	12	7	12.1	5	18	7	12.1	4.2	1.0	4.4
`close`	5	12	7	12.1	5	18	7	12.1	4.2	1.0	4.4
`close_event`	5	12	7	12.1	5	18	7	12.1	4.2	1.0	≤37
`error_event`	5	12	7	12.1	5	18	7	12.1	4.2	1.0	≤37
`extensions`	16	12	8	12.1	6	18	8	12.1	6	1.0	4.4
`message_event`	5	12	7	12.1	5	18	7	12.1	4.2	1.0	≤37
`open_event`	5	12	7	12.1	5	18	7	12.1	4.2	1.0	≤37
`protocol`	15	12	7	12.1	6	18	7	12.1	6	1.0	4.4
`protocol_rfc_6455`	16	12	11	15	6	18	14	14	6	1.0	≤37
`readyState`	5	12	7	12.1	5	18	7	12.1	4.2	1.0	4.4
`send`	5	12	18 11–18 Only parameter of type `ArrayBuffer` and `String` supported. 8–11 Only parameter of type `String` supported. 7–8 Only parameter of type `String` supported. Returns `boolean`.	12.1	5	18	18 14–18 Only parameter of type `ArrayBuffer` and `String` supported. 8–14 Only parameter of type `String` supported. 7–8 Only parameter of type `String` supported. Returns `boolean`.	12.1	4.2	1.0	4.4
`url`	18	12	7	12.1	6	18	7	12.1	6	1.0	4.4
`worker_support`	5	12	37	12.1	5	18	37	12.1	5	1.0	≤37