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⚠️ This is archived documentation for v0.41. Go to the latest version


Experimental module, use at your own risk

While we intend to keep this module as simple and stable as possible, we may need to add features or introduce breaking changes. This could happen at any time until we release this module as stable.

Feel free to provide user feedback, and open an issue or pull request if you have any suggestions.

This experimental API implements the browser's WebSocket API.

With some caveats:

  • The binaryType is by default ArrayBuffer and setting it panics as k6 does not support Blob.
WebSocketConstructs a new WebSocket connection


This example shows:

  • How a single VU can run multiple WebSockets connections asynchronously
  • How to use the timeout and interval functions to stop the connections after some period.
import { randomString, randomIntBetween } from '';
import { WebSocket } from 'k6/experimental/websockets';
import { setTimeout, clearTimeout, setInterval, clearInterval } from 'k6/experimental/timers';
const chatRoomName = 'publicRoom'; // choose any chat room name
const sessionDuration = randomIntBetween(5000, 60000); // user session between 5s and 1m
export default function () {
for (let i = 0; i < 4; i++) {
function startWSWorker(id) {
// create a new websocket connection
const ws = new WebSocket(`wss://${chatRoomName}/`);
ws.addEventListener('open', () => {
// change the user name
ws.send(JSON.stringify({ event: 'SET_NAME', new_name: `Croc ${__VU}:${id}` }));
// listen for messages/errors and log them into console
ws.addEventListener('message', (e) => {
const msg = JSON.parse(;
if (msg.event === 'CHAT_MSG') {
console.log(`VU ${__VU}:${id} received: ${msg.user} says: ${msg.message}`);
} else if (msg.event === 'ERROR') {
console.error(`VU ${__VU}:${id} received:: ${msg.message}`);
} else {
console.log(`VU ${__VU}:${id} received unhandled message: ${msg.message}`);
// send a message every 2-8 seconds
const intervalId = setInterval(() => {
ws.send(JSON.stringify({ event: 'SAY', message: `I'm saying ${randomString(5)}` }));
}, randomIntBetween(2000, 8000)); // say something every 2-8 seconds
// after a sessionDuration stop sending messages and leave the room
const timeout1id = setTimeout(function () {
console.log(`VU ${__VU}:${id}: ${sessionDuration}ms passed, leaving the chat`);
ws.send(JSON.stringify({ event: 'LEAVE' }));
}, sessionDuration);
// after a sessionDuration + 3s close the connection
const timeout2id = setTimeout(function () {
console.log(`Closing the socket forcefully 3s after graceful LEAVE`);
}, sessionDuration + 3000);
// when connection is closing, clean up the previously created timers
ws.addEventListener('close', () => {
console.log(`VU ${__VU}:${id}: disconnected`);