jsdom

What is jsdom?

The jsdom npm package is a pure-JavaScript implementation of many web standards, notably the WHATWG DOM and HTML Standards, for use with Node.js. It is designed to create a web browsing environment similar to what you would find in a web browser, allowing for the parsing and manipulation of HTML and XML documents. It can be used for testing web pages and JavaScript libraries in a Node.js environment.

What are jsdom's main functionalities?

DOM Manipulation

This feature allows you to manipulate the DOM of a document. The code sample demonstrates how to append a new list item to an unordered list.

const { JSDOM } = require('jsdom');
const dom = new JSDOM(`<ul><li>Item 1</li></ul>`);
const ul = dom.window.document.querySelector('ul');
ul.appendChild(dom.window.document.createElement('li')).textContent = 'Item 2';
console.log(dom.window.document.body.innerHTML);

Event Handling

This feature enables you to simulate and handle events. The code sample shows how to simulate a click event on a button and handle it by logging a message.

const { JSDOM } = require('jsdom');
const dom = new JSDOM(`<button id='myButton'>Click me</button>`);
const button = dom.window.document.querySelector('#myButton');
button.addEventListener('click', () => console.log('Button clicked!'));
button.click();

Fetching Remote Content

This feature allows you to fetch remote content and create a JSDOM instance from it. The code sample demonstrates fetching and logging the HTML content of a webpage.

const { JSDOM } = require('jsdom');
JSDOM.fromURL('https://example.com/').then(dom => {
  console.log(dom.serialize());
});

Running Scripts

This feature allows you to run scripts within the context of the JSDOM instance. The code sample shows how to execute a script that changes the text content of the document body.

const { JSDOM } = require('jsdom');
const dom = new JSDOM(`<script>document.body.textContent = 'Hello, world!';</script>`);
console.log(dom.window.document.body.textContent);

Other packages similar to jsdom

cheerio

Cheerio is a fast, flexible, and lean implementation of core jQuery designed specifically for the server. It does not implement a full web browser API as jsdom does, but it is often used for simpler DOM manipulation tasks and is faster due to its focus on a subset of use cases.

puppeteer

Puppeteer is a Node library which provides a high-level API to control Chrome or Chromium over the DevTools Protocol. It is more powerful for tasks like web scraping, automated testing, and rendering since it operates over a real browser, but it is heavier and more resource-intensive compared to jsdom.

phantomjs

PhantomJS is a headless WebKit scriptable with a JavaScript API. It has similar capabilities to Puppeteer but uses WebKit as the rendering engine instead of Chromium. It is no longer actively maintained, but it was once a popular choice for headless website testing.

README

jsdom

A JavaScript implementation of the WHATWG DOM and HTML standards.

Install

$ npm install jsdom

If this gives you trouble with errors about installing Contextify, especially on Windows, see below.

Human contact

see: mailing list

Easymode: jsdom.env

jsdom.env is an API that allows you to throw a bunch of stuff at it, and it will generally do the right thing.

You can use it with a URL

// Count all of the links from the Node.js build page
var jsdom = require("jsdom");

jsdom.env(
  "http://nodejs.org/dist/",
  ["http://code.jquery.com/jquery.js"],
  function (errors, window) {
    console.log("there have been", window.$("a").length, "nodejs releases!");
  }
);

or with raw HTML

// Run some jQuery on a html fragment
var jsdom = require("jsdom");

jsdom.env(
  '<p><a class="the-link" href="https://github.com/tmpvar/jsdom">jsdom!</a></p>',
  ["http://code.jquery.com/jquery.js"],
  function (errors, window) {
    console.log("contents of a.the-link:", window.$("a.the-link").text());
  }
);

or with a configuration object

// Print all of the news items on Hacker News
var jsdom = require("jsdom");

jsdom.env({
  url: "http://news.ycombinator.com/",
  scripts: ["http://code.jquery.com/jquery.js"],
  done: function (errors, window) {
    var $ = window.$;
    console.log("HN Links");
    $("td.title:not(:last) a").each(function() {
      console.log(" -", $(this).text());
    });
  }
});

or with raw JavaScript source

// Print all of the news items on Hacker News
var jsdom = require("jsdom");
var fs = require("fs");
var jquery = fs.readFileSync("./jquery.js", "utf-8");

jsdom.env({
  url: "http://news.ycombinator.com/",
  src: [jquery],
  done: function (errors, window) {
    var $ = window.$;
    console.log("HN Links");
    $("td.title:not(:last) a").each(function () {
      console.log(" -", $(this).text());
    });
  }
});

How it works

The do-what-I-mean API is used like so:

jsdom.env(string, [scripts], [config], callback);

• string: may be a URL, file name, or HTML fragment
• scripts: a string or array of strings, containing file names or URLs that will be inserted as <script> tags
• config: see below
• callback: takes two arguments
  • errors: either null, if nothing goes wrong, or an array of errors
  • window: a brand new window, if there were no loading errors

Example:

jsdom.env(html, function (errors, window) {
  // free memory associated with the window
  window.close();
});

If you would like to specify a configuration object only:

jsdom.env(config);

• config.html: a HTML fragment
• config.file: a file which jsdom will load HTML from; the resulting window's location.href will be a file:// URL.
• config.url: sets the resulting window's location.href; if config.html and config.file are not provided, jsdom will load HTML from this URL.
• config.scripts: see scripts above.
• config.src: an array of JavaScript strings that will be evaluated against the resulting document. Similar to scripts, but it accepts JavaScript instead of paths/URLs.
• config.jar: a custom cookie jar, if desired; see mikeal/request documentation.
• config.parsingMode: either "auto", "html", or "xml". The default is "auto", which uses HTML behavior unless config.url responds with an XML Content-Type, or config.file contains a filename ending in .xml or .xhtml. Setting to "xml" will attempt to parse the document as an XHTML document. (jsdom is currently only OK at doing that.)
• config.document:
  • referrer: the new document will have this referrer.
  • cookie: manually set a cookie value, e.g. 'key=value; expires=Wed, Sep 21 2011 12:00:00 GMT; path=/'.
  • cookieDomain: a cookie domain for the manually set cookie; defaults to 127.0.0.1.
• config.headers: an object giving any headers that will be used while loading the HTML from config.url, if applicable
• config.features: see Flexibility section below. Note: the default feature set for jsdom.env does not include fetching remote JavaScript and executing it. This is something that you will need to carefully enable yourself.
• config.resourceLoader: a function that intercepts subresource requests and allows you to re-route them, modify, or outright replace them with your own content. More below.
• config.done, config.loaded, config.created: see below.

Note that at least one of the callbacks (done, loaded, or created) is required, as is one of html, file, or url.

Initialization lifecycle

If you just want to load the document and execute it, the done callback shown above is the simplest. If anything goes wrong, either while loading the document and creating the window, or while executing any <script>s, the problem will show up in the errors array passed as the first argument.

However, if you want more control over or insight into the initialization lifecycle, you'll want to use the created and/or loaded callbacks:

created(error, window)

The created callback is called as soon as the window is created, or if that process fails. You may access all window properties here; however, window.document is not ready for use yet, as the HTML has not been parsed.

The primary use-case for created is to modify the window object (e.g. add new functions on built-in prototypes) before any scripts execute.

You can also set an event handler for 'load' or other events on the window if you wish. But the loaded callback, below, can be more useful, since it includes script errors.

If the error argument is non-null, it will contain whatever loading error caused the window creation to fail; in that case window will not be passed.

loaded(errors, window)

The loaded callback is called along with the window's 'load' event. This means it will only be called if creation succeeds without error. Note that by the time it has called, any external resources will have been downloaded, and any <script>s will have finished executing.

If errors is non-null, it will contain an array of all JavaScript errors that occured during script execution. window will still be passed, however.

done(errors, window)

Now that you know about created and loaded, you can see that done is essentially both of them smashed together:

• If window creation succeeds and no <script>s cause errors, then errors will be null, and window will be usable.
• If window creation succeeds but there are script errors, then errors will be an array containing those errors, but window will still be usable.
• If window creation fails, then errors will be an array containing the creation error, and window will not be passed.

Migrating from before v1.0.0

If you used jsdom before v1.0.0, it only had a done callback, and it was kind of buggy, sometimes behaving one way, and sometimes another. Due to some excellent work by @Sebmaster in #792, we fixed it up into the above lifecycle. For more information on the migration, see the wiki.

Dealing with asynchronous script loading

If you load scripts asynchronously, e.g. with a module loader like RequireJS, none of the above hooks will really give you what you want. There's nothing, either in jsdom or in browsers, to say "notify me after all asynchronous loads have completed." The solution is to use the mechanisms of the framework you are using to notify about this finishing up. E.g., with RequireJS, you could do

// On the Node side:
var window = jsdom.jsdom(...).parentWindow;
window.onModulesLoaded = function () {
  console.log("ready to roll!");
};

<!-- Inside the HTML you supply to jsdom -->
<script>
requirejs(["entry-module"], function () {
  window.onModulesLoaded();
});
</script>

For more details, see the discussion in #640, especially @matthewkastor's insightful comment.

On running scripts and being safe

By default, jsdom.env will not process and run external JavaScript, since our sandbox is not foolproof. That is, code running inside the DOM's <script>s can, if it tries hard enough, get access to the Node environment, and thus to your machine. If you want to (carefully!) enable running JavaScript, you can use jsdom.jsdom, jsdom.jQueryify, or modify the defaults passed to jsdom.env.

For the hardcore: jsdom.jsdom

The jsdom.jsdom method does less things automatically; it takes in only HTML source, and does not let you to separately supply script that it will inject and execute. It just gives you back a document object, with usable document.parentWindow, and starts asynchronously executing any <script>s included in the HTML source. You can listen for the 'load' event to wait until scripts are done loading and executing, just like you would in a normal HTML page.

Usage of the API generally looks like this:

var jsdom = require("jsdom").jsdom;
var doc = jsdom(markup, options);
var window = doc.parentWindow;

• markup is a HTML document to be parsed. You can also pass undefined to get the basic document, equivalent to what a browser will give if you open up an empty .html file.

• options: see the explanation of the config object above.

Flexibility

One of the goals of jsdom is to be as minimal and light as possible. This section details how someone can change the behavior of Documents before they are created. These features are baked into the DOMImplementation that every Document has, and may be tweaked in two ways:

1. When you create a new Document, by overriding the configuration:

var jsdom = require("jsdom").jsdom;
var doc = jsdom("<html><body></body></html>", {
    features: {
      FetchExternalResources : ["img"]
    }
});

Do note, that this will only affect the document that is currently being created. All other documents will use the defaults specified below (see: Default Features).

1. Before creating any documents, you can modify the defaults for all future documents:

require("jsdom").defaultDocumentFeatures = {
    FetchExternalResources: ["script"],
    ProcessExternalResources: false
};

External Resources

Default features are extremely important for jsdom as they lower the configuration requirement and present developers a set of consistent default behaviors. The following sections detail the available features, their defaults, and the values that jsdom uses.

FetchExternalResources

• Default: ["script"]
• Allowed: ["script", "img", "css", "frame", "iframe", "link"] or false
• Default for jsdom.env: false

Enables/disables fetching files over the file system/HTTP

ProcessExternalResources

• Default: ["script"]
• Allowed: ["script"] or false
• Default for jsdom.env: false

Enables/disables JavaScript execution

SkipExternalResources

• Default: false (allow all)
• Allowed: /url to be skipped/ or false
• Example: /http:\/\/example.org/js/bad\.js/

Filters resource downloading and processing to disallow those matching the given regular expression

Custom External Resource Loader

jsdom lets you intercept subresource requests using config.resourceLoader. config.resourceLoader expects a function which is called for each subresource request with the following arguments:

• resource: a vanilla JavaScript object with the following properties
  • url: a parsed URL object.
  • cookie: the content of the HTTP cookie header (key=value pairs separated by semicolons).
  • cookieDomain: the cookie domain as set in config, defaults to 127.0.0.1.
  • baseUrl: the base URL used to resolve relative URLs.
  • defaultFetch(callback): a convenience method to fetch the resource online.
• callback: a function to be called with two arguments
  • error: either null, if nothing goes wrong, or an Error object.
  • body: a string representing the body of the resource.

For example, fetching all JS files from a different directory and running them in strict mode:

var jsdom = require("jsdom");

jsdom.env({
  url: "http://example.com/",
  resourceLoader: function (resource, callback) {
    var pathname = resource.url.pathname;
    if (/\.js$/.test(pathname)) {
      resource.url.pathname = pathname.replace("/js/", "/js/raw/");
      resource.defaultFetch(function (err, body) {
        if (err) return callback(err);
        callback(null, '"use strict";\n' + body);
      });
    } else {
      resource.defaultFetch(callback);
    }
  },
  features: {
    FetchExternalResources: ["script"],
    ProcessExternalResources: ["script"],
    SkipExternalResources: false
  }
});

Canvas

jsdom includes support for using the canvas package to extend any <canvas> elements with the canvas API. To make this work, you need to include canvas as a dependency in your project, as a peer of jsdom. If jsdom can find the canvas package, it will use it, but if it's not present, then <canvas> elements will behave like <div>s.

More Examples

Creating a browser-like window object

var jsdom = require("jsdom").jsdom;
var document = jsdom("hello world");
var window = document.parentWindow;

console.log(window.document.documentElement.outerHTML);
// output: "<html><head></head><body>hello world</body></html>"

console.log(window.innerWidth);
// output: 1024

console.log(typeof window.document.getElementsByClassName);
// outputs: function

jQueryify

var jsdom = require("jsdom");
var window = jsdom.jsdom().parentWindow;

jsdom.jQueryify(window, "http://code.jquery.com/jquery-2.1.1.js", function () {
  window.$("body").append('<div class="testing">Hello World, It works</div>');

  console.log(window.$(".testing").text());
});

Passing objects to scripts inside the page

var jsdom = require("jsdom").jsdom;
var window = jsdom().parentWindow;

window.__myObject = { foo: "bar" };

var scriptEl = window.document.createElement("script");
scriptEl.src = "anotherScript.js";
window.document.body.appendChild(scriptEl);

// anotherScript.js will have the ability to read `window.__myObject`, even
// though it originated in Node!

Serializing a document

var jsdom = require("jsdom").jsdom;
var serializeDocument = require("jsdom").serializeDocument;

var doc = jsdom("<!DOCTYPE html>hello");

serializeDocument(doc) === "<!DOCTYPE html><html><head></head><body>hello</body></html>";
doc.documentElement.outerHTML === "<html><head></head><body>hello</body></html>";

Capturing Console Output

Forward a window's console output to the Node.js console

var jsdom = require("jsdom");
var window = jsdom.jsdom().parentWindow;

jsdom.getVirtualConsole(window).sendTo(console);

Get an event emitter for a window's console

var jsdom = require("jsdom");
var window = jsdom.jsdom().parentWindow;

var virtualConsole = jsdom.getVirtualConsole(window);

virtualConsole.on("log", function (message) {
  console.log("console.log called ->", message);
});

What Standards Does jsdom Support, Exactly?

Our mission is to get something very close to a headless browser, with emphasis more on the DOM/HTML side of things than the CSS side. As such, our primary goals are supporting The DOM Standard and The HTML Standard. We only support some subset of these so far; in particular we have the subset covered by the outdated DOM 2 spec family down pretty well. We're slowly including more and more from the modern DOM and HTML specs, including some Node APIs, querySelector(All), attribute semantics, the history and URL APIs, and the HTML parsing algorithm.

We also support some subset of the CSSOM, largely via @chad3814's excellent cssstyle package. In general we want to make webpages run headlessly as best we can, and if there are other specs we should be incorporating, let us know.

Contextify

Contextify is a dependency of jsdom, used for running <script> tags within the page. In other words, it allows jsdom, which is run in Node.js, to run strings of JavaScript in an isolated environment that pretends to be a browser environment instead of a server. You can see how this is an important feature.

Unfortunately, doing this kind of magic requires C++. And in Node.js, using C++ from JavaScript means using "native modules." Native modules are compiled at installation time so that they work precisely for your machine; that is, you don't download a contextify binary from npm, but instead build one locally after downloading the source from npm.

Getting C++ compiled within npm's installation system can be tricky, especially for Windows users. Thus, one of the most common problems with jsdom is trying to use it without the proper compilation tools installed. Here's what you need to compile Contextify, and thus to install jsdom:

Windows

• The latest version of Node.js for Windows

• A copy of Visual Studio Express 2013 for Windows Desktop

• A copy of Python 2.7, installed in the default location of C:\Python27

• Set your system environment variable GYP_MSVS_VERSION like so (assuming you have Visual Studio 2013 installed):

  setx GYP_MSVS_VERSION 2013
  

• Restart your command prompt window to ensure required path variables are present.

There are some slight modifications to this that can work; for example other Visual Studio versions often work too. But it's tricky, so start with the basics!

Mac

• XCode needs to be installed
• "Command line tools for XCode" need to be installed
• Launch XCode once to accept the license, etc. and ensure it's properly installed

Linux

You'll need various build tools installed, like make, Python 2.7, and a compiler toolchain. How to install these will be specific to your distro, if you don't already have them.