@mojojs/user-agent

A powerful user-agent for Node.js and browsers. Written in TypeScript. VERY EXPERIMENTAL!

import UserAgent from '@mojojs/user-agent';

const ua = new UserAgent();
const res = await ua.get('https://mojolicious.org');
const dom = await res.html();
const title = dom.at('title').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: 'http://127.0.0.1:3000',

  // Disable TLS certificate validation (only Node.js)
  insecure: true,

  // Keep-alive timeout, disabled with `null`, defaults to 1000 (only Node.js)
  keepAlive: 3000,

  // Maximum number of redirects to follow, defaults to 20 (only Node.js)
  maxRedirects: 5,

  // Name of user-agent to send with `User-Agent` header (only Node.js)
  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('https://mojolicious.org'),

  // 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
  body: 'Some content to send with request',

  // Data structure to be send in JSON format
  json: {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 or `FormData` object to be sent in `multipart/form-data` format
  formData: {fieldA: 'first value', fieldB: 'second value', fieldC: {content: 'third value', filename: 'foo.txt'}},

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

  // An `AbortSignal` to abort the request
  signal: controller.signal
});

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.

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('https://mojolicious.org');
const res = await ua.get('https://mojolicious.org');
const res = await ua.head('https://mojolicious.org');
const res = await ua.options('https://mojolicious.org');
const res = await ua.patch('https://mojolicious.org');
const res = await ua.post('https://mojolicious.org');
const res = await ua.put('https://mojolicious.org');

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

const res = await ua.post('/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.

// ReadableStream
const stream = res.body;

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

// Uint8Array
const data = await res.data();

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

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

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

// `stream.Readable` (only Node.js)
const stream = res.createReadStream();

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

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.

Cookies

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

ua.httpTransport.cookieJar.allowSpecialUseDomain = true;

Of course you can also just disable cookies completely.

ua.httpTransport.cookieJar = null;

In browsers the native browser cookie jar will be used instead.

Hooks

Hooks can be used to extend the user-agent and run code for every HTTP request.

// Add a header to every HTTP request
ua.addHook('request', async (ua, config) => {
  config.headers['X-Bender'] = 'Bite my shiny metal ass!';
});

// Add a query parameter to every HTTP request
ua.addHook('request', async (ua, config) => {
  config.url.searchParams.append('hello', 'mojo');
});

Timeouts

You can use an AbortController to make sure a request does not take longer than a certain amount of time. Once aborted the promise returned by ua.get() will reject.

const controller = new AbortController();
const signal = controller.signal;
setTimeout(() => controller.abort(), 3000);
const res = await ua.get('https://mojojs.org', {signal});

Compression

Responses with gzip or deflate content encoding will be decompressed transparently.

Introspection

With Node.js 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 /hello.html
accept: */*
accept-language: *
sec-fetch-mode: cors
accept-encoding: gzip, deflate

-- Client <<< Server
200 OK
Content-Type: text/plain; charset=utf-8
Content-Length: 12
Date: Mon, 02 May 2022 23:32:34 GMT
Connection: close

Hello World!

Installation

All you need is Node.js 18 (or newer).

$ npm install @mojojs/user-agent

Support

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