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docs: provide README for jest-haste-map package (#14613)
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Mutesa-Cedric authored Oct 12, 2023
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# jest-haste-map

`jest-haste-map` is a module used by Jest, a popular JavaScript testing framework, to create a fast lookup of files in a project. It helps Jest efficiently locate and track changes in files during testing, making it particularly useful for large projects with many files.

## why jest-haste-map ?

- **Parallel crawling and analysis:** jest-haste-map crawls the entire project, extracts dependencies, and analyzes files in parallel across worker processes.This can significantly improve the performance of the map building process.
- **Cached file system:** jest-haste-map keeps a cache of the file system in memory and on disk. This allows for fast file related operations, such as resolving module imports and checking for changes.
- **Minimal work**: jest-haste-map only does the minimal amount of work necessary when files change. (If you are using [watchman](https://facebook.github.io/watchman/) (recommended for large projects), Jest will ask watchman for changed files instead of crawling the file system. This is very fast even if you have tens of thousands of files.)
- **File system watching:** jest-haste-map can watch the file system for changes. This is useful for building interactive tools, such as watch mode.

## Installation

with npm :

```bash
npm install jest-haste-map --save-dev
```

with yarn :

```bash
yarn add jest-haste-map --dev
```

## usage

`jest-haste-map` is compatible with both `ES modules` and `CommonJS`

### simple usage

```javascript
const map = new HasteMap.default({
// options
});
```

### Example usage (get all files with .js extension in the project)

```javascript
import HasteMap from 'jest-haste-map';
import os from 'os';
import {dirname} from 'path';
import {fileURLToPath} from 'url';

const root = dirname(fileURLToPath(import.meta.url));

const map = new HasteMap.default({
id: 'myproject', //Used for caching.
extensions: ['js'], // Tells jest-haste-map to only crawl .js files.
maxWorkers: os.availableParallelism(), //Parallelizes across all available CPUs.
platforms: [], // This is only used for React Native, you can leave it empty.
roots: [root], // Can be used to only search a subset of files within `rootDir`
retainAllFiles: true,
rootDir: root, //The project root.
});

const {hasteFS} = await map.build();

const files = hasteFS.getAllFiles();

console.log(files);
```
### options
| Option | Type | Required | Default Value |
| ---------------------- | ------------------- | -------- | ------------- |
| cacheDirectory | string | No | `os.tmpdir()` |
| computeDependencies | boolean | No | `true` |
| computeSha1 | boolean | No | `false` |
| console | Console | No | - |
| dependencyExtractor | string \| null | No | `null` |
| enableSymlinks | boolean | No | `false` |
| extensions | Array<string> | Yes | - |
| forceNodeFilesystemAPI | boolean | Yes | - |
| hasteImplModulePath | string | Yes | - |
| hasteMapModulePath | string | Yes | - |
| id | string | Yes | - |
| ignorePattern | HasteRegExp | No | - |
| maxWorkers | number | Yes | - |
| mocksPattern | string | No | - |
| platforms | Array<string> | Yes | - |
| resetCache | boolean | No | - |
| retainAllFiles | boolean | Yes | - |
| rootDir | string | Yes | - |
| roots | Array<string> | Yes | - |
| skipPackageJson | boolean | Yes | - |
| throwOnModuleCollision | boolean | Yes | - |
| useWatchman | boolean | No | `true` |
For more, you can check [github](https://github.com/jestjs/jest/tree/main/packages/jest-haste-map)

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