JavaScript API

The init context (aka "init code") is code in the global context that has access to a few functions not accessible during main script execution (aka "VU context" or "VU code"). For a more detailed description see Running k6.

The k6 module contains k6-specific functionality.

The k6/crypto module provides common hashing functionality available in the GoLang crypto package.

The encoding module provides base64 encoding/decoding as defined by RFC4648.

The k6/html module contains functionality for HTML parsing.

The k6/http module contains functionality for performing HTTP transactions.

The metrics module provides functionality to create custom metrics of various types. All metrics (both the built-in ones and the custom ones) have a type. There are four different metrics types, and they are: Counter, Gauge, Rate and Trend.

All values added to a custom metric can optionally be tagged which can be very useful when analysing the results after a test run.

Example

import { Counter, Gauge, Rate, Trend } from 'k6/metrics';
import { check } from 'k6';

var myCounter = new Counter('my_counter');
var myGauge = new Gauge('my_gauge');
var myRate = new Rate('my_rate');
var myTrend = new Trend('my_trend');

export default function() {
  myCounter.add(1);
  myCounter.add(2, { tag1: 'myValue', tag2: 'myValue2' });

  myGauge.add(123);
  myGauge.add(456, { tag1: 'myValue', tag2: 'myValue2' });

  myRate.add(true);
  myRate.add(false, { tag1: 'value', tag2: 'value2' });

  myTrend.add(1);
  myTrend.add(2, { tag1: 'value', tag2: 'value2' });
}

The ws module provides a WebSocket client implementing the WebSocket protocol.

WebSocket built-in metrics

k6 will automatically collect some metrics when interacting with a WebSocket service through the k6/ws API.

Check out the Results output article for more information about how to process the metric information.

Example

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

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

  var 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 });
}
//VU execution won't be completely finished until the connection is closed.

Error codes, introduced in k6 0.24.0, are unique numbers that can be used to identify and handle different application and network errors more easily. For the moment, these error codes are applicable only for errors that happen during HTTP requests, but they will be reused and extended to support other protocols in future k6 releases.

When an error occurs, its code is determined and returned as both the error_code field of the http.Response object, and also attached as the error_code tag to any metrics associated with that request. Additionally, for more details, the error metric tag and http.Response field will still contain the actual string error message.

Error codes for different errors are as distinct as possible, but for easier handling and grouping, codes in different error categories are also grouped in broad ranges. The current error code ranges are:

• 1000-1099 - General errors
• 1100-1199 - DNS errors
• 1200-1299 - TCP errors
• 1300-1399 - TLS errors
• 1400-1499 - HTTP 4xx errors
• 1500-1599 - HTTP 5xx errors
• 1600-1699 - HTTP/2 specific errors

The following specific error codes are currently defined:

• 1000: A generic error that isn't any of the ones listed below.
• 1010: A non-TCP network error - this is a place holder there is no error currently known to trigger it.
• 1100: A generic DNS error that isn't any of the ones listed below.
• 1101: No IP for the provided host was found.
• 1110: Blacklisted IP was resolved or a connection to such was tried to be established.
• 1200: A generic TCP error that isn't any of the ones listed below.
• 1201: A "broken pipe" on write - the other side has likely closed the connection.
• 1202: An unknown TCP error - We got an error that we don't recognize but it is from the operating system and has errno set on it. The message in error includes the operation(write,read) and the errno, the OS, and the original message of the error.
• 1210: General TCP dial error.
• 1211: Dial timeout error - the timeout for the dial was reached.
• 1212: Dial connection refused - the connection was refused by the other party on dial.
• 1220: Reset by peer - the connection was reset by the other party, most likely a server.
• 1300: General TLS error
• 1310: Unknown authority - the certificate issuer is unknown.
• 1311: The certificate doesn't match the hostname.
• 1400 to 1499: error codes that correspond to the HTTP 4xx status codes for client errors
• 1500 to 1599: error codes that correspond to the HTTP 5xx status codes for server errors
• 1600: A generic HTTP/2 error that isn't any of the ones listed below.
• 1610: A general HTTP/2 GoAway error.
• 1611 to 1629: HTTP/2 GoAway errors with the value of the specific HTTP/2 error code added to 1611.
• 1630: A general HTTP/2 stream error.
• 1631 to 1649: HTTP/2 stream errors with the value of the specific HTTP/2 error code added to 1631.
• 1650: A general HTTP/2 connection error.
• 1651 to 1669: HTTP/2 connection errors with the value of the specific HTTP/2 error code added to 1651.