Cloudflare Docs
Visit Workers on GitHub
Set theme to dark (⇧+D)



WebSockets allow you to communicate in real time with your Cloudflare Workers serverless functions.


// { 0: <WebSocket>, 1: <WebSocket> }
let websocketPair = new WebSocketPair();

The WebSocketPair returned from this constructor is an Object, with two WebSockets at keys 0 and 1.

These WebSockets are commonly referred to as client and server. The below example combines Object.values and ES6 destructuring to retrieve the WebSockets as client and server:

let [client, server] = Object.values(new WebSocketPair());



  • accept()

    • Accepts the Websocket connection and begins terminating requests for the WebSocket at Cloudflare’s edge. This effectively enables the Workers runtime to begin responding to and handling WebSocket requests.


  • addEventListener(eventWebSocketEvent, callbackFunctionFunction)

    • Add callback functions to be executed when an event has occurred on the WebSocket.


  • event WebSocketEvent

    • The WebSocket event (refer to Events) to listen to.
  • callbackFunction(message Message ) Function

    • A function to be called when the WebSocket responds to a specific event.


  • close(codenumber, reasonstring)

    Close the WebSocket connection.


  • codeinteger optional

  • reasonstring optional

    • A human-readable string indicating why the WebSocket connection was closed.


  • send(messagestring)

    Send a message to the other WebSocket in this WebSocket pair.


  • messagestring

    • The message to send down the WebSocket connection to the corresponding client. This should be a string or something coercible into a string; for example, strings and numbers will be simply cast into strings, but objects and arrays should be cast to JSON strings using JSON.stringify, and parsed in the client.


  • close

An event indicating the WebSocket has closed.

  • error

An event indicating there was an error with the WebSocket.

  • message

An event indicating a new message received from the client, including the data passed by the client.



  • data any - The data passed back from the other WebSocket in your pair.
  • type string - Defaults to message.