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1<h1 align="center">
2 <img width="100" height="100" src="logo.svg" alt=""><br>
3 jsdom
4</h1>
5
6jsdom is a pure-JavaScript implementation of many web standards, notably the WHATWG [DOM](https://dom.spec.whatwg.org/) and [HTML](https://html.spec.whatwg.org/multipage/) Standards, for use with Node.js. In general, the goal of the project is to emulate enough of a subset of a web browser to be useful for testing and scraping real-world web applications.
7
8The latest versions of jsdom require Node.js v12 or newer. (Versions of jsdom below v17 still work with previous Node.js versions, but are unsupported.)
9
10## Basic usage
11
12```js
13const jsdom = require("jsdom");
14const { JSDOM } = jsdom;
15```
16
17To use jsdom, you will primarily use the `JSDOM` constructor, which is a named export of the jsdom main module. Pass the constructor a string. You will get back a `JSDOM` object, which has a number of useful properties, notably `window`:
18
19```js
20const dom = new JSDOM(`<!DOCTYPE html><p>Hello world</p>`);
21console.log(dom.window.document.querySelector("p").textContent); // "Hello world"
22```
23
24(Note that jsdom will parse the HTML you pass it just like a browser does, including implied `<html>`, `<head>`, and `<body>` tags.)
25
26The resulting object is an instance of the `JSDOM` class, which contains a number of useful properties and methods besides `window`. In general, it can be used to act on the jsdom from the "outside," doing things that are not possible with the normal DOM APIs. For simple cases, where you don't need any of this functionality, we recommend a coding pattern like
27
28```js
29const { window } = new JSDOM(`...`);
30// or even
31const { document } = (new JSDOM(`...`)).window;
32```
33
34Full documentation on everything you can do with the `JSDOM` class is below, in the section "`JSDOM` Object API".
35
36## Customizing jsdom
37
38The `JSDOM` constructor accepts a second parameter which can be used to customize your jsdom in the following ways.
39
40### Simple options
41
42```js
43const dom = new JSDOM(``, {
44 url: "https://example.org/",
45 referrer: "https://example.com/",
46 contentType: "text/html",
47 includeNodeLocations: true,
48 storageQuota: 10000000
49});
50```
51
52- `url` sets the value returned by `window.location`, `document.URL`, and `document.documentURI`, and affects things like resolution of relative URLs within the document and the same-origin restrictions and referrer used while fetching subresources. It defaults to `"about:blank"`.
53- `referrer` just affects the value read from `document.referrer`. It defaults to no referrer (which reflects as the empty string).
54- `contentType` affects the value read from `document.contentType`, as well as how the document is parsed: as HTML or as XML. Values that are not a [HTML mime type](https://mimesniff.spec.whatwg.org/#html-mime-type) or an [XML mime type](https://mimesniff.spec.whatwg.org/#xml-mime-type) will throw. It defaults to `"text/html"`. If a `charset` parameter is present, it can affect [binary data processing](#encoding-sniffing).
55- `includeNodeLocations` preserves the location info produced by the HTML parser, allowing you to retrieve it with the `nodeLocation()` method (described below). It also ensures that line numbers reported in exception stack traces for code running inside `<script>` elements are correct. It defaults to `false` to give the best performance, and cannot be used with an XML content type since our XML parser does not support location info.
56- `storageQuota` is the maximum size in code units for the separate storage areas used by `localStorage` and `sessionStorage`. Attempts to store data larger than this limit will cause a `DOMException` to be thrown. By default, it is set to 5,000,000 code units per origin, as inspired by the HTML specification.
57
58Note that both `url` and `referrer` are canonicalized before they're used, so e.g. if you pass in `"https:example.com"`, jsdom will interpret that as if you had given `"https://example.com/"`. If you pass an unparseable URL, the call will throw. (URLs are parsed and serialized according to the [URL Standard](https://url.spec.whatwg.org/).)
59
60### Executing scripts
61
62jsdom's most powerful ability is that it can execute scripts inside the jsdom. These scripts can modify the content of the page and access all the web platform APIs jsdom implements.
63
64However, this is also highly dangerous when dealing with untrusted content. The jsdom sandbox is not foolproof, and code running inside the DOM's `<script>`s can, if it tries hard enough, get access to the Node.js environment, and thus to your machine. As such, the ability to execute scripts embedded in the HTML is disabled by default:
65
66```js
67const dom = new JSDOM(`<body>
68 <script>document.body.appendChild(document.createElement("hr"));</script>
69</body>`);
70
71// The script will not be executed, by default:
72dom.window.document.body.children.length === 1;
73```
74
75To enable executing scripts inside the page, you can use the `runScripts: "dangerously"` option:
76
77```js
78const dom = new JSDOM(`<body>
79 <script>document.body.appendChild(document.createElement("hr"));</script>
80</body>`, { runScripts: "dangerously" });
81
82// The script will be executed and modify the DOM:
83dom.window.document.body.children.length === 2;
84```
85
86Again we emphasize to only use this when feeding jsdom code you know is safe. If you use it on arbitrary user-supplied code, or code from the Internet, you are effectively running untrusted Node.js code, and your machine could be compromised.
87
88If you want to execute _external_ scripts, included via `<script src="">`, you'll also need to ensure that they load them. To do this, add the option `resources: "usable"` [as described below](#loading-subresources). (You'll likely also want to set the `url` option, for the reasons discussed there.)
89
90Event handler attributes, like `<div onclick="">`, are also governed by this setting; they will not function unless `runScripts` is set to `"dangerously"`. (However, event handler _properties_, like `div.onclick = ...`, will function regardless of `runScripts`.)
91
92If you are simply trying to execute script "from the outside", instead of letting `<script>` elements and event handlers attributes run "from the inside", you can use the `runScripts: "outside-only"` option, which enables fresh copies of all the JavaScript spec-provided globals to be installed on `window`. This includes things like `window.Array`, `window.Promise`, etc. It also, notably, includes `window.eval`, which allows running scripts, but with the jsdom `window` as the global:
93
94```js
95const { window } = new JSDOM(``, { runScripts: "outside-only" });
96
97window.eval(`document.body.innerHTML = "<p>Hello, world!</p>";`);
98window.document.body.children.length === 1;
99```
100
101This is turned off by default for performance reasons, but is safe to enable.
102
103(Note that in the default configuration, without setting `runScripts`, the values of `window.Array`, `window.eval`, etc. will be the same as those provided by the outer Node.js environment. That is, `window.eval === eval` will hold, so `window.eval` will not run scripts in a useful way.)
104
105We strongly advise against trying to "execute scripts" by mashing together the jsdom and Node global environments (e.g. by doing `global.window = dom.window`), and then executing scripts or test code inside the Node global environment. Instead, you should treat jsdom like you would a browser, and run all scripts and tests that need access to a DOM inside the jsdom environment, using `window.eval` or `runScripts: "dangerously"`. This might require, for example, creating a browserify bundle to execute as a `<script>` element—just like you would in a browser.
106
107Finally, for advanced use cases you can use the `dom.getInternalVMContext()` method, documented below.
108
109### Pretending to be a visual browser
110
111jsdom does not have the capability to render visual content, and will act like a headless browser by default. It provides hints to web pages through APIs such as `document.hidden` that their content is not visible.
112
113When the `pretendToBeVisual` option is set to `true`, jsdom will pretend that it is rendering and displaying content. It does this by:
114
115* Changing `document.hidden` to return `false` instead of `true`
116* Changing `document.visibilityState` to return `"visible"` instead of `"prerender"`
117* Enabling `window.requestAnimationFrame()` and `window.cancelAnimationFrame()` methods, which otherwise do not exist
118
119```js
120const window = (new JSDOM(``, { pretendToBeVisual: true })).window;
121
122window.requestAnimationFrame(timestamp => {
123 console.log(timestamp > 0);
124});
125```
126
127Note that jsdom still [does not do any layout or rendering](#unimplemented-parts-of-the-web-platform), so this is really just about _pretending_ to be visual, not about implementing the parts of the platform a real, visual web browser would implement.
128
129### Loading subresources
130
131#### Basic options
132
133By default, jsdom will not load any subresources such as scripts, stylesheets, images, or iframes. If you'd like jsdom to load such resources, you can pass the `resources: "usable"` option, which will load all usable resources. Those are:
134
135* Frames and iframes, via `<frame>` and `<iframe>`
136* Stylesheets, via `<link rel="stylesheet">`
137* Scripts, via `<script>`, but only if `runScripts: "dangerously"` is also set
138* Images, via `<img>`, but only if the `canvas` npm package is also installed (see "[Canvas Support](#canvas-support)" below)
139
140When attempting to load resources, recall that the default value for the `url` option is `"about:blank"`, which means that any resources included via relative URLs will fail to load. (The result of trying to parse the URL `/something` against the URL `about:blank` is an error.) So, you'll likely want to set a non-default value for the `url` option in those cases, or use one of the [convenience APIs](#convenience-apis) that do so automatically.
141
142#### Advanced configuration
143
144_This resource loader system is new as of jsdom v12.0.0, and we'd love your feedback on whether it meets your needs and how easy it is to use. Please file an issue to discuss!_
145
146To more fully customize jsdom's resource-loading behavior, you can pass an instance of the `ResourceLoader` class as the `resources` option value:
147
148```js
149const resourceLoader = new jsdom.ResourceLoader({
150 proxy: "http://127.0.0.1:9001",
151 strictSSL: false,
152 userAgent: "Mellblomenator/9000",
153});
154const dom = new JSDOM(``, { resources: resourceLoader });
155```
156
157The three options to the `ResourceLoader` constructor are:
158
159- `proxy` is the address of an HTTP proxy to be used.
160- `strictSSL` can be set to false to disable the requirement that SSL certificates be valid.
161- `userAgent` affects the `User-Agent` header sent, and thus the resulting value for `navigator.userAgent`. It defaults to <code>\`Mozilla/5.0 (${process.platform || "unknown OS"}) AppleWebKit/537.36 (KHTML, like Gecko) jsdom/${jsdomVersion}\`</code>.
162
163You can further customize resource fetching by subclassing `ResourceLoader` and overriding the `fetch()` method. For example, here is a version that only returns results for requests to a trusted origin:
164
165```js
166class CustomResourceLoader extends jsdom.ResourceLoader {
167 fetch(url, options) {
168 // Override the contents of this script to do something unusual.
169 if (url === "https://example.com/some-specific-script.js") {
170 return Promise.resolve(Buffer.from("window.someGlobal = 5;"));
171 }
172
173 return super.fetch(url, options);
174 }
175}
176```
177
178jsdom will call your custom resource loader's `fetch()` method whenever it encounters a "usable" resource, per the above section. The method takes a URL string, as well as a few options which you should pass through unmodified if calling `super.fetch()`. It must return a promise for a Node.js `Buffer` object, or return `null` if the resource is intentionally not to be loaded. In general, most cases will want to delegate to `super.fetch()`, as shown.
179
180One of the options you will receive in `fetch()` will be the element (if applicable) that is fetching a resource.
181
182```js
183class CustomResourceLoader extends jsdom.ResourceLoader {
184 fetch(url, options) {
185 if (options.element) {
186 console.log(`Element ${options.element.localName} is requesting the url ${url}`);
187 }
188
189 return super.fetch(url, options);
190 }
191}
192```
193
194### Virtual consoles
195
196Like web browsers, jsdom has the concept of a "console". This records both information directly sent from the page, via scripts executing inside the document, as well as information from the jsdom implementation itself. We call the user-controllable console a "virtual console", to distinguish it from the Node.js `console` API and from the inside-the-page `window.console` API.
197
198By default, the `JSDOM` constructor will return an instance with a virtual console that forwards all its output to the Node.js console. To create your own virtual console and pass it to jsdom, you can override this default by doing
199
200```js
201const virtualConsole = new jsdom.VirtualConsole();
202const dom = new JSDOM(``, { virtualConsole });
203```
204
205Code like this will create a virtual console with no behavior. You can give it behavior by adding event listeners for all the possible console methods:
206
207```js
208virtualConsole.on("error", () => { ... });
209virtualConsole.on("warn", () => { ... });
210virtualConsole.on("info", () => { ... });
211virtualConsole.on("dir", () => { ... });
212// ... etc. See https://console.spec.whatwg.org/#logging
213```
214
215(Note that it is probably best to set up these event listeners *before* calling `new JSDOM()`, since errors or console-invoking script might occur during parsing.)
216
217If you simply want to redirect the virtual console output to another console, like the default Node.js one, you can do
218
219```js
220virtualConsole.sendTo(console);
221```
222
223There is also a special event, `"jsdomError"`, which will fire with error objects to report errors from jsdom itself. This is similar to how error messages often show up in web browser consoles, even if they are not initiated by `console.error`. So far, the following errors are output this way:
224
225- Errors loading or parsing subresources (scripts, stylesheets, frames, and iframes)
226- Script execution errors that are not handled by a window `onerror` event handler that returns `true` or calls `event.preventDefault()`
227- Not-implemented errors resulting from calls to methods, like `window.alert`, which jsdom does not implement, but installs anyway for web compatibility
228
229If you're using `sendTo(c)` to send errors to `c`, by default it will call `c.error(errorStack[, errorDetail])` with information from `"jsdomError"` events. If you'd prefer to maintain a strict one-to-one mapping of events to method calls, and perhaps handle `"jsdomError"`s yourself, then you can do
230
231```js
232virtualConsole.sendTo(c, { omitJSDOMErrors: true });
233```
234
235### Cookie jars
236
237Like web browsers, jsdom has the concept of a cookie jar, storing HTTP cookies. Cookies that have a URL on the same domain as the document, and are not marked HTTP-only, are accessible via the `document.cookie` API. Additionally, all cookies in the cookie jar will impact the fetching of subresources.
238
239By default, the `JSDOM` constructor will return an instance with an empty cookie jar. To create your own cookie jar and pass it to jsdom, you can override this default by doing
240
241```js
242const cookieJar = new jsdom.CookieJar(store, options);
243const dom = new JSDOM(``, { cookieJar });
244```
245
246This is mostly useful if you want to share the same cookie jar among multiple jsdoms, or prime the cookie jar with certain values ahead of time.
247
248Cookie jars are provided by the [tough-cookie](https://www.npmjs.com/package/tough-cookie) package. The `jsdom.CookieJar` constructor is a subclass of the tough-cookie cookie jar which by default sets the `looseMode: true` option, since that [matches better how browsers behave](https://github.com/whatwg/html/issues/804). If you want to use tough-cookie's utilities and classes yourself, you can use the `jsdom.toughCookie` module export to get access to the tough-cookie module instance packaged with jsdom.
249
250### Intervening before parsing
251
252jsdom allows you to intervene in the creation of a jsdom very early: after the `Window` and `Document` objects are created, but before any HTML is parsed to populate the document with nodes:
253
254```js
255const dom = new JSDOM(`<p>Hello</p>`, {
256 beforeParse(window) {
257 window.document.childNodes.length === 0;
258 window.someCoolAPI = () => { /* ... */ };
259 }
260});
261```
262
263This is especially useful if you are wanting to modify the environment in some way, for example adding shims for web platform APIs jsdom does not support.
264
265## `JSDOM` object API
266
267Once you have constructed a `JSDOM` object, it will have the following useful capabilities:
268
269### Properties
270
271The property `window` retrieves the `Window` object that was created for you.
272
273The properties `virtualConsole` and `cookieJar` reflect the options you pass in, or the defaults created for you if nothing was passed in for those options.
274
275### Serializing the document with `serialize()`
276
277The `serialize()` method will return the [HTML serialization](https://html.spec.whatwg.org/#html-fragment-serialisation-algorithm) of the document, including the doctype:
278
279```js
280const dom = new JSDOM(`<!DOCTYPE html>hello`);
281
282dom.serialize() === "<!DOCTYPE html><html><head></head><body>hello</body></html>";
283
284// Contrast with:
285dom.window.document.documentElement.outerHTML === "<html><head></head><body>hello</body></html>";
286```
287
288### Getting the source location of a node with `nodeLocation(node)`
289
290The `nodeLocation()` method will find where a DOM node is within the source document, returning the [parse5 location info](https://www.npmjs.com/package/parse5#options-locationinfo) for the node:
291
292```js
293const dom = new JSDOM(
294 `<p>Hello
295 <img src="foo.jpg">
296 </p>`,
297 { includeNodeLocations: true }
298);
299
300const document = dom.window.document;
301const bodyEl = document.body; // implicitly created
302const pEl = document.querySelector("p");
303const textNode = pEl.firstChild;
304const imgEl = document.querySelector("img");
305
306console.log(dom.nodeLocation(bodyEl)); // null; it's not in the source
307console.log(dom.nodeLocation(pEl)); // { startOffset: 0, endOffset: 39, startTag: ..., endTag: ... }
308console.log(dom.nodeLocation(textNode)); // { startOffset: 3, endOffset: 13 }
309console.log(dom.nodeLocation(imgEl)); // { startOffset: 13, endOffset: 32 }
310```
311
312Note that this feature only works if you have set the `includeNodeLocations` option; node locations are off by default for performance reasons.
313
314### Interfacing with the Node.js `vm` module using `getInternalVMContext()`
315
316The built-in [`vm`](https://nodejs.org/api/vm.html) module of Node.js is what underpins jsdom's script-running magic. Some advanced use cases, like pre-compiling a script and then running it multiple times, benefit from using the `vm` module directly with a jsdom-created `Window`.
317
318To get access to the [contextified global object](https://nodejs.org/api/vm.html#vm_what_does_it_mean_to_contextify_an_object), suitable for use with the `vm` APIs, you can use the `getInternalVMContext()` method:
319
320```js
321const { Script } = require("vm");
322
323const dom = new JSDOM(``, { runScripts: "outside-only" });
324const script = new Script(`
325 if (!this.ran) {
326 this.ran = 0;
327 }
328
329 ++this.ran;
330`);
331
332const vmContext = dom.getInternalVMContext();
333
334script.runInContext(vmContext);
335script.runInContext(vmContext);
336script.runInContext(vmContext);
337
338console.assert(dom.window.ran === 3);
339```
340
341This is somewhat-advanced functionality, and we advise sticking to normal DOM APIs (such as `window.eval()` or `document.createElement("script")`) unless you have very specific needs.
342
343Note that this method will throw an exception if the `JSDOM` instance was created without `runScripts` set, or if you are [using jsdom in a web browser](#running-jsdom-inside-a-web-browser).
344
345### Reconfiguring the jsdom with `reconfigure(settings)`
346
347The `top` property on `window` is marked `[Unforgeable]` in the spec, meaning it is a non-configurable own property and thus cannot be overridden or shadowed by normal code running inside the jsdom, even using `Object.defineProperty`.
348
349Similarly, at present jsdom does not handle navigation (such as setting `window.location.href = "https://example.com/"`); doing so will cause the virtual console to emit a `"jsdomError"` explaining that this feature is not implemented, and nothing will change: there will be no new `Window` or `Document` object, and the existing `window`'s `location` object will still have all the same property values.
350
351However, if you're acting from outside the window, e.g. in some test framework that creates jsdoms, you can override one or both of these using the special `reconfigure()` method:
352
353```js
354const dom = new JSDOM();
355
356dom.window.top === dom.window;
357dom.window.location.href === "about:blank";
358
359dom.reconfigure({ windowTop: myFakeTopForTesting, url: "https://example.com/" });
360
361dom.window.top === myFakeTopForTesting;
362dom.window.location.href === "https://example.com/";
363```
364
365Note that changing the jsdom's URL will impact all APIs that return the current document URL, such as `window.location`, `document.URL`, and `document.documentURI`, as well as the resolution of relative URLs within the document, and the same-origin checks and referrer used while fetching subresources. It will not, however, perform navigation to the contents of that URL; the contents of the DOM will remain unchanged, and no new instances of `Window`, `Document`, etc. will be created.
366
367## Convenience APIs
368
369### `fromURL()`
370
371In addition to the `JSDOM` constructor itself, jsdom provides a promise-returning factory method for constructing a jsdom from a URL:
372
373```js
374JSDOM.fromURL("https://example.com/", options).then(dom => {
375 console.log(dom.serialize());
376});
377```
378
379The returned promise will fulfill with a `JSDOM` instance if the URL is valid and the request is successful. Any redirects will be followed to their ultimate destination.
380
381The options provided to `fromURL()` are similar to those provided to the `JSDOM` constructor, with the following additional restrictions and consequences:
382
383- The `url` and `contentType` options cannot be provided.
384- The `referrer` option is used as the HTTP `Referer` request header of the initial request.
385- The `resources` option also affects the initial request; this is useful if you want to, for example, configure a proxy (see above).
386- The resulting jsdom's URL, content type, and referrer are determined from the response.
387- Any cookies set via HTTP `Set-Cookie` response headers are stored in the jsdom's cookie jar. Similarly, any cookies already in a supplied cookie jar are sent as HTTP `Cookie` request headers.
388
389### `fromFile()`
390
391Similar to `fromURL()`, jsdom also provides a `fromFile()` factory method for constructing a jsdom from a filename:
392
393```js
394JSDOM.fromFile("stuff.html", options).then(dom => {
395 console.log(dom.serialize());
396});
397```
398
399The returned promise will fulfill with a `JSDOM` instance if the given file can be opened. As usual in Node.js APIs, the filename is given relative to the current working directory.
400
401The options provided to `fromFile()` are similar to those provided to the `JSDOM` constructor, with the following additional defaults:
402
403- The `url` option will default to a file URL corresponding to the given filename, instead of to `"about:blank"`.
404- The `contentType` option will default to `"application/xhtml+xml"` if the given filename ends in `.xht`, `.xhtml`, or `.xml`; otherwise it will continue to default to `"text/html"`.
405
406### `fragment()`
407
408For the very simplest of cases, you might not need a whole `JSDOM` instance with all its associated power. You might not even need a `Window` or `Document`! Instead, you just need to parse some HTML, and get a DOM object you can manipulate. For that, we have `fragment()`, which creates a `DocumentFragment` from a given string:
409
410```js
411const frag = JSDOM.fragment(`<p>Hello</p><p><strong>Hi!</strong>`);
412
413frag.childNodes.length === 2;
414frag.querySelector("strong").textContent === "Hi!";
415// etc.
416```
417
418Here `frag` is a [`DocumentFragment`](https://developer.mozilla.org/en-US/docs/Web/API/DocumentFragment) instance, whose contents are created by parsing the provided string. The parsing is done using a `<template>` element, so you can include any element there (including ones with weird parsing rules like `<td>`). It's also important to note that the resulting `DocumentFragment` will not have [an associated browsing context](https://html.spec.whatwg.org/multipage/#concept-document-bc): that is, elements' `ownerDocument` will have a null `defaultView` property, resources will not load, etc.
419
420All invocations of the `fragment()` factory result in `DocumentFragment`s that share the same template owner `Document`. This allows many calls to `fragment()` with no extra overhead. But it also means that calls to `fragment()` cannot be customized with any options.
421
422Note that serialization is not as easy with `DocumentFragment`s as it is with full `JSDOM` objects. If you need to serialize your DOM, you should probably use the `JSDOM` constructor more directly. But for the special case of a fragment containing a single element, it's pretty easy to do through normal means:
423
424```js
425const frag = JSDOM.fragment(`<p>Hello</p>`);
426console.log(frag.firstChild.outerHTML); // logs "<p>Hello</p>"
427```
428
429## Other noteworthy features
430
431### Canvas support
432
433jsdom includes support for using the [`canvas`](https://www.npmjs.com/package/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. Since jsdom v13, version 2.x of `canvas` is required; version 1.x is no longer supported.
434
435### Encoding sniffing
436
437In addition to supplying a string, the `JSDOM` constructor can also be supplied binary data, in the form of a Node.js [`Buffer`](https://nodejs.org/docs/latest/api/buffer.html) or a standard JavaScript binary data type like `ArrayBuffer`, `Uint8Array`, `DataView`, etc. When this is done, jsdom will [sniff the encoding](https://html.spec.whatwg.org/multipage/syntax.html#encoding-sniffing-algorithm) from the supplied bytes, scanning for `<meta charset>` tags just like a browser does.
438
439If the supplied `contentType` option contains a `charset` parameter, that encoding will override the sniffed encoding—unless a UTF-8 or UTF-16 BOM is present, in which case those take precedence. (Again, this is just like a browser.)
440
441This encoding sniffing also applies to `JSDOM.fromFile()` and `JSDOM.fromURL()`. In the latter case, any `Content-Type` headers sent with the response will take priority, in the same fashion as the constructor's `contentType` option.
442
443Note that in many cases supplying bytes in this fashion can be better than supplying a string. For example, if you attempt to use Node.js's `buffer.toString("utf-8")` API, Node.js will not strip any leading BOMs. If you then give this string to jsdom, it will interpret it verbatim, leaving the BOM intact. But jsdom's binary data decoding code will strip leading BOMs, just like a browser; in such cases, supplying `buffer` directly will give the desired result.
444
445### Closing down a jsdom
446
447Timers in the jsdom (set by `window.setTimeout()` or `window.setInterval()`) will, by definition, execute code in the future in the context of the window. Since there is no way to execute code in the future without keeping the process alive, outstanding jsdom timers will keep your Node.js process alive. Similarly, since there is no way to execute code in the context of an object without keeping that object alive, outstanding jsdom timers will prevent garbage collection of the window on which they are scheduled.
448
449If you want to be sure to shut down a jsdom window, use `window.close()`, which will terminate all running timers (and also remove any event listeners on the window and document).
450
451### Running jsdom inside a web browser
452
453jsdom has some support for being run inside a web browser, using [browserify](https://browserify.org/). That is, inside a web browser, you can use a browserified jsdom to create an entirely self-contained set of plain JavaScript objects which look and act much like the browser's existing DOM objects, while being entirely independent of them. "Virtual DOM", indeed!
454
455jsdom's primary target is still Node.js, and so we use language features that are only present in recent Node.js versions (namely, Node.js v8+). Thus, older browsers will likely not work. (Even transpilation will not help: we use `Proxy`s extensively throughout the jsdom codebase.)
456
457Notably, jsdom works well inside a web worker. The original contributor, [@lawnsea](https://github.com/lawnsea/), who made this possible, has [published a paper](https://pdfs.semanticscholar.org/47f0/6bb6607a975500a30e9e52d7c9fbc0034e27.pdf) about his project which uses this capability.
458
459Not everything works perfectly when running jsdom inside a web browser. Sometimes that is because of fundamental limitations (such as not having filesystem access), but sometimes it is simply because we haven't spent enough time making the appropriate small tweaks. Bug reports are certainly welcome.
460
461### Debugging the DOM using Chrome Devtools
462
463As of Node.js v6 you can debug programs using Chrome Devtools. See the [official documentation](https://nodejs.org/en/docs/inspector/) for how to get started.
464
465By default jsdom elements are formatted as plain old JS objects in the console. To make it easier to debug, you can use [jsdom-devtools-formatter](https://github.com/viddo/jsdom-devtools-formatter), which lets you inspect them like real DOM elements.
466
467## Caveats
468
469### Asynchronous script loading
470
471People often have trouble with asynchronous script loading when using jsdom. Many pages load scripts asynchronously, but there is no way to tell when they're done doing so, and thus when it's a good time to run your code and inspect the resulting DOM structure. This is a fundamental limitation; we cannot predict what scripts on the web page will do, and so cannot tell you when they are done loading more scripts.
472
473This can be worked around in a few ways. The best way, if you control the page in question, is to use whatever mechanisms are given by the script loader to detect when loading is done. For example, if you're using a module loader like RequireJS, the code could look like:
474
475```js
476// On the Node.js side:
477const window = (new JSDOM(...)).window;
478window.onModulesLoaded = () => {
479 console.log("ready to roll!");
480};
481```
482
483```html
484<!-- Inside the HTML you supply to jsdom -->
485<script>
486requirejs(["entry-module"], () => {
487 window.onModulesLoaded();
488});
489</script>
490```
491
492If you do not control the page, you could try workarounds such as polling for the presence of a specific element.
493
494For more details, see the discussion in [#640](https://github.com/jsdom/jsdom/issues/640), especially [@matthewkastor](https://github.com/matthewkastor)'s [insightful comment](https://github.com/jsdom/jsdom/issues/640#issuecomment-22216965).
495
496### Unimplemented parts of the web platform
497
498Although we enjoy adding new features to jsdom and keeping it up to date with the latest web specs, it has many missing APIs. Please feel free to file an issue for anything missing, but we're a small and busy team, so a pull request might work even better.
499
500Beyond just features that we haven't gotten to yet, there are two major features that are currently outside the scope of jsdom. These are:
501
502- **Navigation**: the ability to change the global object, and all other objects, when clicking a link or assigning `location.href` or similar.
503- **Layout**: the ability to calculate where elements will be visually laid out as a result of CSS, which impacts methods like `getBoundingClientRects()` or properties like `offsetTop`.
504
505Currently jsdom has dummy behaviors for some aspects of these features, such as sending a "not implemented" `"jsdomError"` to the virtual console for navigation, or returning zeros for many layout-related properties. Often you can work around these limitations in your code, e.g. by creating new `JSDOM` instances for each page you "navigate" to during a crawl, or using `Object.defineProperty()` to change what various layout-related getters and methods return.
506
507Note that other tools in the same space, such as PhantomJS, do support these features. On the wiki, we have a more complete writeup about [jsdom vs. PhantomJS](https://github.com/jsdom/jsdom/wiki/jsdom-vs.-PhantomJS).
508
509## Supporting jsdom
510
511jsdom is a community-driven project maintained by a team of [volunteers](https://github.com/orgs/jsdom/people). You could support jsdom by:
512
513- [Getting professional support for jsdom](https://tidelift.com/subscription/pkg/npm-jsdom?utm_source=npm-jsdom&utm_medium=referral&utm_campaign=readme) as part of a Tidelift subscription. Tidelift helps making open source sustainable for us while giving teams assurances for maintenance, licensing, and security.
514- [Contributing](https://github.com/jsdom/jsdom/blob/master/Contributing.md) directly to the project.
515
516## Getting help
517
518If you need help with jsdom, please feel free to use any of the following venues:
519
520- The [mailing list](https://groups.google.com/group/jsdom) (best for "how do I" questions)
521- The [issue tracker](https://github.com/jsdom/jsdom/issues) (best for bug reports)
522- The Matrix room: [#jsdom:matrix.org](https://matrix.to/#/#jsdom:matrix.org)