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

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