How can I extend WebSocket types in Node.js using TypeScript?

Question

I am trying to extend the following WebSocket https://github.com/DefinitelyTyped/DefinitelyTyped/blob/master/types/ws/index.d.ts

Whatever I try, I cannot seem to add a new property to the WebSocket

// Messes with other typings in the WebSocket
declare module "ws" {
  // Tried declare class MyWebSocket extends WebSocket too
  interface WebSocket {
    id: string;
  }
}

wss.on("connection", socket => {
  const id = uuidv4();
  socket.id = id

  socket.on("message", data => {

I saw multiple people having this issue online but I could not find a detailed solution

hoangdv · Accepted Answer · 2020-03-30 15:51:45Z

7

Create a custom interface - ExtWebSocket, the interface will extend WebSocket. Then cast your socket as ExtWebSocket. No need declare module.

interface ExtWebSocket extends WebSocket {
  id: string; // your custom property
}

Usage

wss.on("connection", (socket: ExtWebSocket) => { // here
  const id = uuidv4();
  socket.id = id;

  socket.on("message", data => {
    // do something
  })
});

edited Mar 30, 2020 at 15:51

answered Mar 30, 2020 at 15:35

hoangdv

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4 Comments

user13103906 Over a year ago

This gives me Property 'on' does not exist on type 'MyWebSocket'

hoangdv Over a year ago

Are your sure MyWebSocket extends WebSocket

user13103906 Over a year ago

Turns out I had to "allowSyntheticDefaultImports": true and import it, otherwise it picked up the WebSocket from Node I think, thanks!

glenatron Over a year ago

In order to stop TypeScript complaining about the wss.handleUpgrade callback I had to add the type to the server, like this: private wss = new Server<ExtWebSocket>({port: 3033})

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