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jsdom
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jsdom 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.
The 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.)
## Basic usage
```js
const jsdom = require("jsdom");
const { JSDOM } = jsdom;
```
To 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`:
```js
const dom = new JSDOM(`<!DOCTYPE html><p>Hello world</p>`);
console.log(dom.window.document.querySelector("p").textContent); // "Hello world"
```
(Note that jsdom will parse the HTML you pass it just like a browser does, including implied `<html>`, `<head>`, and `<body>` tags.)
The 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
```js
const { window } = new JSDOM(`...`);
// or even
const { document } = (new JSDOM(`...`)).window;
```
Full documentation on everything you can do with the `JSDOM` class is below, in the section "`JSDOM` Object API".
## Customizing jsdom
The `JSDOM` constructor accepts a second parameter which can be used to customize your jsdom in the following ways.
### Simple options
```js
const dom = new JSDOM(``, {
url: "https://example.org/",
referrer: "https://example.com/",
contentType: "text/html",
includeNodeLocations: true,
storageQuota: 10000000
});
```
- `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"`.
- `referrer` just affects the value read from `document.referrer`. It defaults to no referrer (which reflects as the empty string).
- `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).
- `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.
- `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.
Note 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/).)
### Executing scripts
jsdom'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.
However, 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:
```js
const dom = new JSDOM(`<body>
<script>document.body.appendChild(document.createElement("hr"));</script>
</body>`);
// The script will not be executed, by default:
dom.window.document.body.children.length === 1;
```
To enable executing scripts inside the page, you can use the `runScripts: "dangerously"` option:
```js
const dom = new JSDOM(`<body>
<script>document.body.appendChild(document.createElement("hr"));</script>
</body>`, { runScripts: "dangerously" });
// The script will be executed and modify the DOM:
dom.window.document.body.children.length === 2;
```
Again 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.
If 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.)
Event 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`.)
If 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:
```js
const { window } = new JSDOM(``, { runScripts: "outside-only" });
window.eval(`document.body.innerHTML = "<p>Hello, world!</p>";`);
window.document.body.children.length === 1;
```
This is turned off by default for performance reasons, but is safe to enable.
(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.)
We 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.
Finally, for advanced use cases you can use the `dom.getInternalVMContext()` method, documented below.
### Pretending to be a visual browser
jsdom 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.
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