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Update to the browser testing recipe to use jsdom directly
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DavidVujic committed Sep 19, 2022
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# Setting up AVA for browser testing

Translations: [Español](https://github.com/avajs/ava-docs/blob/main/es_ES/docs/recipes/browser-testing.md), [Français](https://github.com/avajs/ava-docs/blob/main/fr_FR/docs/recipes/browser-testing.md), [Italiano](https://github.com/avajs/ava-docs/blob/main/it_IT/docs/recipes/browser-testing.md), [Русский](https://github.com/avajs/ava-docs/blob/main/ru_RU/docs/recipes/browser-testing.md), [简体中文](https://github.com/avajs/ava-docs/blob/main/zh_CN/docs/recipes/browser-testing.md)
AVA is running in a __Node.js__ environment. JavaScript that runs in a browser will likely expect the browser DOM globals to be in place.
With help from a package called [jsdom](https://github.com/jsdom/jsdom),
you can write unit tests with `ava` also for JavaScript that will run in a browser
and relying on browser specific globals such as `window`, `document` and `navigator`.

AVA does not support running tests in browsers [yet](https://github.com/avajs/ava/issues/24). However JavaScript libraries that require browser specific globals (`window`, `document`, `navigator`, etc) can still be tested with AVA by mocking these globals.
## Install jsdom

This recipe works for any library that needs a mocked browser environment.

## Install browser-env

> **❗️ Important note**
>
>`browser-env` adds properties from the `jsdom` window namespace to the Node.js global namespace. This is explicitly [recommended against](https://github.com/tmpvar/jsdom/wiki/Don't-stuff-jsdom-globals-onto-the-Node-global) by `jsdom`. Please read through the linked wiki page and make sure you understand the caveats. If you don't have lots of dependencies that also require a browser environment then [`window`](https://github.com/lukechilds/window#universal-testing-pattern) may be a better solution.
Install [browser-env](https://github.com/lukechilds/browser-env).

> Simulates a global browser environment using jsdom.
```
$ npm install --save-dev browser-env
```bash
npm install --save-dev jsdom
```

## Setup browser-env

Create a helper file, prefixed with an underscore. This ensures AVA does not treat it as a test.
## Writing unit tests

`test/_setup-browser-env.js`:
Use `jsdom` to set the globals and the DOM elements that the test target is expecting.

```js
import browserEnv from 'browser-env';
browserEnv();
```

By default, `browser-env` will add all global browser variables to the Node.js global scope, creating a full browser environment. This should have good compatibility with most front-end libraries, however, it's generally not a good idea to create lots of global variables if you don't need to. If you know exactly which browser globals you need, you can pass an array of them.
### An example Unit Test
The JavaScript code to be tested is doing a DOM query, such as: `document.querySelector('#my-element-id')`.

```js
import browserEnv from 'browser-env';
browserEnv(['window', 'document', 'navigator']);
```

You can expose more global variables by assigning them to the `global` object. For instance, jQuery is typically available through the `$` variable:

```js
import browserEnv from 'browser-env';
import jQuery from 'jquery';

browserEnv();
global.$ = jQuery(window);
```

## Configure tests to use browser-env

Configure AVA to `require` the helper before every test file.

**`package.json`:**

```json
{
"ava": {
"require": [
"./test/_setup-browser-env.js"
]
}
}
```

## Enjoy!

Write your tests and enjoy a mocked browser environment.

`test.js`:
To make the code testable with `ava`, add the element to `jsdom` and set the global object.

```js
import test from 'ava';
import { JSDOM } from 'jsdom';

test('Insert to DOM', t => {
const div = document.createElement('div');
document.body.appendChild(div);
test.before(() => {
const dom = new JSDOM('<div id="my-element-id" />'); // insert any html needed for the unit test suite here
global.document = dom.window.document; // add the globals needed for the unit tests in this suite.
});

test('this is an example', (t) => {
const res = myTarget.runFunctionThatExpectsTheDocumentGlobalAndElement();

t.is(document.querySelector('div'), div);
t.truthy(res);
});
```

## Important note
In general, adding globals to the `Node.js` environment is [recommended against](https://github.com/jsdom/jsdom/wiki/Don't-stuff-jsdom-globals-onto-the-Node-global) by `jsdom`.
Please read through the linked wiki page and make sure you understand why.

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