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Socket.on(event, callback)

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

Parameter Type Description
event string The event name to define a callback for.
callback 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 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.


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

export default function() {
  var url = 'ws://';
  var params = { tags: { my_tag: 'hello' } };

  var response = ws.connect(url, params, function(socket) {
    socket.on('open', function open() {

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

    socket.on('ping', function() {

    socket.on('pong', function() {

    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() {

    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');
    }, 2000);

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