The mojo.js toolkit contains a full featured HTTP and WebSocket user agent. And while its primary purpose is integration testing of web applications, it can also be used for many other things.

import {UserAgent} from '@mojojs/core';

const ua = new UserAgent();
const res = await ua.get('');
const content = await res.text();

The API is heavily inspired by the Fetch Standard and should feel familar if you've used fetch before.

User-Agent Options

The user agent can be initialized with a few options, but none of them are required.

const ua = new UserAgent({

  // Base URL to be used to resolve all relative request URLs with
  baseURL: '',

  // Maximum number of redirects to follow, default to none
  maxRedirects: 5,

  // Name of user agent to send with `User-Agent` header
  name: 'mojoUA/1.0'

Request Config

Every request is represented by a config object that contains various properties to describe every part of the HTTP request.

const res = await ua.request({

  // HTTP method for request
  method: 'GET',

  // URL of request target as a string or URL object, may be be relative to `ua.baseURL`
  url: new URL(''),

  // Headers to include in request
  headers: {Accept: '*/*', Authorization: 'token 123456789abcdef'},

  // Object with key/value pairs to be sent with the query string
  query: {fieldA: 'first value', fieldB: 'second value'},

  // Request body as a string, `Buffer` or `stream.Readable` object
  body: 'Some content to send with request',

  // Data structure to be sent in JSON format, or for WebSockets a `true` value to enable JSON mode
  json: {hello: ['world']},

  // Data structure to be sent in YAML format
  yaml: {hello: ['world']},

  // Object with key/value pairs to be sent in `application/x-www-form-urlencoded` format
  form: {fieldA: 'first value', fieldB: 'second value'},

  // Object with key/value pairs and a file upload to be sent in `multipart/form-data` format
  formData: {fieldA: 'first value', fieldB: 'second value', fieldC: {content: 'Hello Mojo!', filename: 'test.txt'}},

  // Basic authentication
  auth: 'user:password',

  // Disable TLS certificate validation
  insecure: true,

  // Override the trusted CA certificates (defaults to CAs curated by Mozilla that ship with Node)
  ca: ['...', '...'],

  // Server name for the SNI (Server Name Indication) TLS extension
  servername: 'localhost',

  // Path to UNIX domain socket (UNIX only)
  socketPath: '/var/lib/run/myapp.sock',

  // Alternative `http.Agent` object to use, for keep-alive or SOCKS proxy support with `proxy-agent`
  // (this API is likely to change in mojo.js 2.0)
  agent: new http.Agent({keepAlive: true})

The request method returns a Promise that resolves with a response object, right after the response status line and headers have been received. But before any data from the response body has been read, which can be handled in a separate step later on. Be aware: The agent API is likely to change in mojo.js 2.0 to improve compatibility with fetch based backends.

Request Shortcuts

Since every request includes at least method and url values, there are HTTP method specific shortcuts you can use instead of request.

const res = await ua.delete('');
const res = await ua.get('');
const res = await ua.head('');
const res = await ua.options('');
const res = await ua.patch('');
const res = await'');
const res = await ua.put('');

All remaining config values can be passed with a second argument to any one of the shortcut methods.

const res = await'/search', {form: {q: 'mojo'}});

Response Headers

Status line information and response headers are available right away with the response object.

// Status code and message
const statusCode = res.statusCode;
const statusMessage = res.statusMessage;

// Headers
const contentType = res.get('Content-Type');

// 2xx
const isSuccess = res.isSuccess;

// 3xx
const isRedirect = res.isRedirect;

// 4xx
const isClientError = res.isClientError;

// 5xx
const isServerError = res.isServerError;

// 4xx or 5xx
const isError = res.isError;

Response Body

The reponse body can be received in various formats. Most of them will result once again in a new Promise, resolving to different results however.

// String
const text = await res.text();

// Buffer
const buffer = await res.buffer();

// Pipe content to `stream.Writable` object
await res.pipe(process.stdout);

// Parsed JSON
const data = await res.json();

// Parsed YAML
const data = await res.yaml();

// Parsed HTML via `@mojojs/dom`
const dom = await res.html();
const title ='title').text();

// Parsed XML via `@mojojs/dom`
const dom = await res.xml();

// Async iterator
const parts = [];
for await (const chunk of res) {
const buffer = Buffer.concat(parts);

For HTML and XML parsing @mojojs/dom will be used. Making it very easy to extract information from documents with just a CSS selector and almost no code at all.


By default a tough-cookie based cookie jar will be used for state keeping, and you can reconfigure it however you like. = true;

Of course you can also just disable cookies completely.

const ua = new UserAgent({cookieJar: null});


For WebSocket handshakes there are also quite a few options available.

const ws = await ua.websocket('wss://', {

  // Headers to include in handshake
  headers: {Accept: '*/*', Authorization: 'token 123456789abcdef'},

  // Object with key/value pairs to be sent with the query string
  query: {fieldA: 'first value', fieldB: 'second value'},

  // Enable JSON mode (encoding and decoding all messages automatically)
  json: true,

  // Basic authentication
  auth: 'user:password',

  // WebSocket subprotocols
  protocols: ['foo', 'bar'],

  // Path to UNIX domain socket (UNIX only)
  socketPath: '/var/lib/run/myapp.sock'

You can choose between multiple API styles.

// Async iterator
const ws = await ua.websocket('/ws');
await ws.send('something');
for await (const message of ws) {

// Events (this API is likely to change in mojo.js 2.0)
const ws = await ua.websocket('/ws');
await ws.send('something');
ws.on('message', message => {

With support for ping and pong frames. Be aware: The event based API is likely to change in mojo.js 2.0 to imporve browser compatibility.

// Handshake with authentication headers (this API is likely to change in mojo.js 2.0)
const ws = await ua.websocket('/ws', {headers: {Authorization: 'token 123456789abcdef'}});
ws.on('ping', data => {

Cookies from the cookie jar will of course also be available for the handshake, so you can rely on them for things like authentication.


For web application testing there is also a more specialised subclass available that adds various test methods using assert to integrate seamlessly into most testing frameworks.

import {TestUserAgent} from '@mojojs/core';

const ua = new TestUserAgent({baseURL: ''});
(await ua.getOk('/')).statusIs(200).headerLike('Content-Type', /html/).bodyLike(/Mojolicious/);

tap subtests are also supported, and scope changes can be managed automatically with the tap option.

import {TestUserAgent} from '@mojojs/core';
import t from 'tap';

t.test('Mojolicious', async t => {
  const ua = new TestUserAgent({baseURL: '', tap: t});

  await t.test('Index', async t => {
    (await ua.getOk('/')).statusIs(200).bodyLike(/Mojolicious/);

And to test mojo.js web applications there is no need to mock anything. The test user agent can automatically start and manage a web server listening to a random port for you.

import {app} from '../index.js';
import t from 'tap';

t.test('Example application', async t => {
  const ua = await app.newTestUserAgent({tap: t});

  await t.test('Index', async t => {
    (await ua.getOk('/')).statusIs(200).bodyLike(/mojo.js/);

  await ua.stop();

There are test alternatives for all HTTP method shortcuts.

await ua.deleteOk('/foo');
await ua.getOk('/foo', {headers: {Host: ''}});
await ua.headOk('/foo', {headers: {Accept: '*/*'}});
await ua.optionsOk('/foo', {auth: 'kraih:s3cret'});
await ua.patchOk('/foo', {formData: {role: 'admin'}});
await ua.postOk('/foo', {body: Buffer.from('Hello Mojo!')});
await ua.putOk('/foo', {json: {hello: 'world'}});

await ua.websocketOk('/ws', {protocols: ['test/1', 'test/2']});

All test methods return the user agent object again to allow for easy method chaining and all state is stored inside the user agent object.

// Status tests
(await ua.getOk('/foo'))

// Header tests
(await ua.getOk('/foo'))
  .headerIs('Content-Type', 'text/html')
  .headerLike('Content-Type', /html/)

// Body tests
(await ua.getOk('/foo'))
  .bodyIs('Hello World!')

// JSON tests
(await ua.getOk('/foo'))
  .jsonIs({hello: 'world'})
  .jsonIs('world', '/hello');

// YAML tests
(await ua.getOk('/foo'))
  .yamlIs({hello: 'world'})
  .yamlIs('world', '/hello');

// HTML tests
(await ua.getOk('/foo'))
  .elementExists('head > title')
  .elementExistsNot('body #error')
  .textLike('head > title', /Welcome/);

Testing WebSockets is almost as easy, but all operations are async and have to return a Promise.

await ua.websocketOk('/echo');
await ua.sendOk('hello');
assert.equal(await ua.messageOk(), 'echo: hello');
await ua.closeOk(4000);
await ua.closedOk(4000);

And while the test user agent is very efficient for testing backend services, for frontend testing we recommend combining it with playwright.


You can set the MOJO_CLIENT_DEBUG environment variable to get some advanced diagnostics information printed to STDERR.

$ MOJO_CLIENT_DEBUG=1 node myapp.js
-- Client >>> Server
GET / HTTP/1.1\x0d
Accept-Encoding: gzip\x0d
Connection: close\x0d
-- Client <<< Server
HTTP/1.1 200 OK\x0d
Content-Type: text/plain; charset=utf-8\x0d
Content-Length: 12\x0d
Date: Mon, 02 May 2022 23:32:34 GMT\x0d
Connection: close\x0d
Hello World!

Be aware: The exact output format is likely to change over time as more protocols are supported.


A lot more documentation and examples by many different authors can be found in the mojo.js wiki.


If you have any questions the documentation might not yet answer, don't hesitate to ask in the Forum, on Matrix, or IRC.