WebSocket on Grafana Labs

WebSocket.addEventListener(event, handler)

Mon, 21 Sep 2026 15:16:28 +0000

WebSocket.addEventListener(event, handler)

Set up handler functions for various events on the WebSocket connection. You can define multiple handlers for the same event.

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

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 WebSocket.close() or when the server sends the `close` event with code status 1000 (normal closure).
error	Emitted when an error occurs.

Example

A k6 script that demonstrates how to add multiple event listeners for the WebSocket message connection event.

import { WebSocket } from 'k6/websockets';

export default function () {
  const ws = new WebSocket('ws://localhost:10000');
  ws.binaryType = 'arraybuffer';

  ws.onopen = () => {
    console.log('connected');
    ws.send(Date.now().toString());
  };

  ws.onmessage = () => {
    console.log('onmessage event handler!');
  };

  // Multiple event handlers on the same event
  ws.addEventListener('message', () => {
    console.log('addEventListener event handler!');

    ws.close();
  });
}

The preceding example uses a WebSocket echo server, which you can run with the following command:

docker run --detach --rm --name ws-echo-server -p 10000:8080 jmalloc/echo-server

WebSocket.send(data)

Mon, 21 Sep 2026 15:16:28 +0000

WebSocket.send(data)

Send data through the connection. You can use JSON.stringify to convert a JSON or JavaScript values to a JSON string.

Parameter	Type	Description
data	string / ArrayBuffer / Blob / ArrayBufferView	The data to send.

Example

A k6 script that demonstrates how to add an event listener for the open WebSocket connection event sends a message and closes the connection.

import { WebSocket } from 'k6/websockets';

export default function () {
  const ws = new WebSocket('ws://localhost:10000');

  ws.onopen = () => {
    ws.send('lorem ipsum');
    ws.close();
  };
}

The preceding example uses a WebSocket echo server, which you can run with the following command:

docker run --detach --rm --name ws-echo-server -p 10000:8080 jmalloc/echo-server

WebSocket.close([code])

Mon, 21 Sep 2026 15:16:28 +0000

WebSocket.close([code])

Close the WebSocket connection.

Parameter	Type	Description
code (optional)	number	WebSocket status code. (default: 1000) . See the list of supported close codes.

Example

A k6 script that initiates a WebSocket connection and closes it using the onopen handler.

import { WebSocket } from 'k6/websockets';

export default function () {
  const ws = new WebSocket('ws://localhost:10000');

  ws.onopen = () => {
    ws.close();
    console.log('connection closed');
  };
}

The preceding example uses a WebSocket echo server, which you can run with the following command:

docker run --detach --rm --name ws-echo-server -p 10000:8080 jmalloc/echo-server

WebSocket.ping()

Mon, 21 Sep 2026 15:16:28 +0000

WebSocket.ping()

Send a ping. You can use ping messages to verify that the remote endpoint is responsive.

Example

A k6 script that initiates a WebSocket connection, sends a ping, and closes it using the onopen handler. The console should log connection is alive, since the recipient should automatically emit the pong event.

import { WebSocket } from 'k6/websockets';

export default function () {
  const ws = new WebSocket('ws://localhost:10000');

  ws.onopen = () => {
    console.log('WebSocket connection established!');
    ws.ping();
    ws.close();
  };

  ws.onpong = () => {
    // As required by the spec, when the ping is received, the recipient must send back a pong.
    console.log('connection is alive');
  };
}

The preceding example uses a WebSocket echo server, which you can run with the following command:

docker run --detach --rm --name ws-echo-server -p 10000:8080 jmalloc/echo-server

WebSocket.onclose

Mon, 21 Sep 2026 15:16:28 +0000

WebSocket.onclose

A handler for a WebSocket connection close event. For multiple, simultaneous event handlers, use WebSocket.addEventListener().

Example

A k6 script that initiates a WebSocket connection, sends a ping, and closes it using onopen handler. The console should also log WebSocket connection closed from the onclose handler.

import { WebSocket } from 'k6/websockets';

export default function () {
  const ws = new WebSocket('ws://localhost:10000');

  ws.onopen = () => {
    console.log('WebSocket connection established!');
    ws.close();
  };

  ws.onclose = () => {
    console.log('WebSocket connection closed!');
  };
}

The preceding example uses a WebSocket echo server, which you can run with the following command:

docker run --detach --rm --name ws-echo-server -p 10000:8080 jmalloc/echo-server

WebSocket.onerror

Mon, 21 Sep 2026 15:16:28 +0000

WebSocket.onerror

A handler for a WebSocket connection error event. For multiple, simultaneous event handlers, use WebSocket.addEventListener().

Example

A k6 script that initiates a WebSocket connection and sets up a handler for the error event.

import { WebSocket } from 'k6/websockets';

export default function () {
  const ws = new WebSocket('ws://localhost:10000');

  ws.onerror = (e) => {
    console.log(e);
    ws.close();
  };
}

The preceding example uses a WebSocket echo server, which you can run with the following command:

docker run --detach --rm --name ws-echo-server -p 10000:8080 jmalloc/echo-server

WebSocket.onmessage

Mon, 21 Sep 2026 15:16:28 +0000

WebSocket.onmessage

A handler for a WebSocket connection message event. For multiple, simultaneous event handlers, use WebSocket.addEventListener().

Example

A k6 script that initiates a WebSocket connection and sets up a handler for the message event.

import { WebSocket } from 'k6/websockets';

export default function () {
  const ws = new WebSocket('ws://localhost:10000');
  ws.binaryType = 'arraybuffer';

  ws.onmessage = (data) => {
    console.log('a message received');
    console.log(data);
    ws.close();
  };
}

The preceding example uses a WebSocket echo server, which you can run with the following command:

docker run --detach --rm --name ws-echo-server -p 10000:8080 jmalloc/echo-server

WebSocket.onopen

Mon, 21 Sep 2026 15:16:28 +0000

WebSocket.onopen

A handler for a WebSocket connection open event. For multiple, simultaneous event handlers, use WebSocket.addEventListener().

Example

A k6 script that initiates a WebSocket connection and sets up a handler for the open event.

import { WebSocket } from 'k6/websockets';

export default function () {
  const ws = new WebSocket('ws://localhost:10000');

  ws.onopen = () => {
    console.log('WebSocket connection established!');
    ws.close();
  };
}

The preceding example uses a WebSocket echo server, which you can run with the following command:

docker run --detach --rm --name ws-echo-server -p 10000:8080 jmalloc/echo-server

WebSocket.onping

Mon, 21 Sep 2026 15:16:28 +0000

WebSocket.onping

A handler for a WebSocket connection ping event. For multiple, simultaneous event handlers, use WebSocket.addEventListener().

Example

A k6 script that initiates a WebSocket connection and sets up a handler for the ping event.

import { WebSocket } from 'k6/websockets';

export default function () {
  const ws = new WebSocket('wss://quickpizza.grafana.com/ws');

  ws.onping = () => {
    console.log('A ping happened!');
    ws.close();
  };

  ws.onclose = () => {
    console.log('WebSocket connection closed!');
  };

  ws.onopen = () => {
    ws.send(JSON.stringify({ event: 'SET_NAME', new_name: `Croc ${__VU}` }));
  };
  ws.onerror = (err) => {
    console.log(err);
  };
}

WebSocket.onpong

Mon, 21 Sep 2026 15:16:28 +0000

WebSocket.onpong

A handler for a WebSocket connection pong event. For multiple, simultaneous event handlers, use WebSocket.addEventListener().

Example

A k6 script that initiates a WebSocket connection and setups a handler for the pong event.

import { WebSocket } from 'k6/websockets';

export default function () {
  const ws = new WebSocket('ws://localhost:10000');

  ws.onpong = () => {
    console.log('A pong happened!');
    ws.close();
  };

  ws.onopen = () => {
    ws.ping();
  };
}

The preceding example uses a WebSocket echo server, which you can run with the following command:

docker run --detach --rm --name ws-echo-server -p 10000:8080 jmalloc/echo-server