WebSocket

BaselineWidely available *

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

* Some parts of this feature may have varying levels of support.

Note: This feature is available inWeb Workers.

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

To construct aWebSocket, use theWebSocket() constructor.

Note:TheWebSocket API has no way to applybackpressure, therefore when messages arrive faster than the application can process them, the application will either fill up the device's memory by buffering those messages, become unresponsive due to 100% CPU usage, or both. For an alternative that provides backpressure automatically, seeWebSocketStream.

Constructor

WebSocket(): Returns a newly createdWebSocket object.

Instance properties

WebSocket.binaryType: The binary data type used by the connection.
WebSocket.bufferedAmountRead only: The number of bytes of queued data.
WebSocket.extensionsRead only: The extensions selected by the server.
WebSocket.protocolRead only: The sub-protocol selected by the server.
WebSocket.readyStateRead only: The current state of the connection.
WebSocket.urlRead 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 usingaddEventListener() or by assigning an event listener to theoneventname property of this interface.

close: Fired when a connection with aWebSocket is closed.Also available via theonclose property
error: Fired when a connection with aWebSocket has been closed because of an error, such as when some data couldn't be sent.Also available via theonerror property.
message: Fired when data is received through aWebSocket.Also available via theonmessage property.
open: Fired when a connection with aWebSocket is opened.Also available via theonopen property.

Examples

// Create WebSocket connection.const socket = new WebSocket("ws://localhost:8080");// Connection openedsocket.addEventListener("open", (event) => {  socket.send("Hello Server!");});// Listen for messagessocket.addEventListener("message", (event) => {  console.log("Message from server ", event.data);});