---
title: "Socket.on(event, callback) | Grafana k6 documentation"
description: "Set up callback functions for various events on the WebSocket connection."
---

# Socket.on(event, callback)

> Note
> 
> A module with a better and standard API exists.
> 
> The new [k6/websockets API](/docs/k6/latest/javascript-api/k6-websockets/) partially implements the [WebSockets API living standard](https://websockets.spec.whatwg.org/).
> 
> When possible, we recommend using the new API. It uses a global event loop for consistency with other k6 APIs and better performance.

Set up callback functions for various events on the WebSocket connection. Multiple handlers can be defined for the same event.

Expand table

| Parameter | Type     | Description                                  |
|-----------|----------|----------------------------------------------|
| event     | string   | The event name to define a callback for.     |
| callback  | function | The function to call when the event happens. |

Expand table

| Event name | Description                                                                                                                                                                                                        |
|------------|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| open       | Emitted when the connection is established                                                                                                                                                                         |
| message    | Emitted when a message is received from the server.                                                                                                                                                                |
| ping       | Emitted when a ping is received from the server. The client will automatically send back a `pong`.                                                                                                                 |
| pong       | Emitted when a pong is received from the server.                                                                                                                                                                   |
| close      | Emitted when the connection is closed by the client [Socket.close()](/docs/k6/latest/javascript-api/k6-ws/socket/socket-close/) or when the server sends the `close` event with code status 1000 (normal closure). |
| error      | Emitted when an error occurs. Non-normal closure errors will be forwarded.                                                                                                                                         |

### Example

JavaScript ![Copy code to clipboard](/media/images/icons/icon-copy-small-2.svg) Copy

```javascript
import ws from 'k6/ws';
import { check } from 'k6';

export default function () {
  const url = 'wss://echo.websocket.org';
  const params = { tags: { my_tag: 'hello' } };

  const response = ws.connect(url, params, function (socket) {
    socket.on('open', function open() {
      console.log('connected');
      socket.send(Date.now());

      socket.setInterval(function timeout() {
        socket.ping();
        console.log('Pinging every 1sec (setInterval test)');
      }, 1000);
    });

    socket.on('ping', function () {
      console.log('PING!');
    });

    socket.on('pong', function () {
      console.log('PONG!');
    });

    socket.on('pong', function () {
      // Multiple event handlers on the same event
      console.log('OTHER PONG!');
    });

    socket.on('message', function (message) {
      console.log(`Received message: ${message}`);
    });

    socket.on('close', function () {
      console.log('disconnected');
    });

    socket.on('error', function (e) {
      if (e.error() != 'websocket: close sent') {
        console.log('An unexpected error occured: ', e.error());
      }
    });

    socket.setTimeout(function () {
      console.log('2 seconds passed, closing the socket');
      socket.close();
    }, 2000);
  });

  check(response, { 'status is 101': (r) => r && r.status === 101 });
}
```