unionfs

What is unionfs?

The unionfs npm package allows you to create a union of multiple file systems, enabling you to overlay one file system on top of another. This can be useful for combining different sources of files or for creating a virtual file system that merges multiple directories.

What are unionfs's main functionalities?

Union of Multiple File Systems

This feature allows you to combine multiple file systems into a single unified file system. In this example, the native file system and an in-memory file system are combined, allowing you to read from both as if they were one.

const { ufs } = require('unionfs');
const fs = require('fs');
const memfs = require('memfs');

ufs
  .use(fs)  // Use the native file system
  .use(memfs);  // Use an in-memory file system

// Now you can read from both file systems
ufs.readFileSync('/path/to/file');

Overlay File Systems

This feature allows you to overlay one file system on top of another. In this example, an in-memory file system is overlaid on top of the native file system, allowing you to write to the in-memory file system and read from the overlaid file system.

const { ufs } = require('unionfs');
const fs = require('fs');
const memfs = require('memfs');

ufs
  .use(memfs)  // Use an in-memory file system
  .use(fs);  // Overlay the native file system

// Write to the in-memory file system
memfs.writeFileSync('/path/to/file', 'Hello World');

// Read from the overlaid file system
console.log(ufs.readFileSync('/path/to/file', 'utf8'));

Other packages similar to unionfs

memfs

memfs is a JavaScript implementation of an in-memory file system. It allows you to create a virtual file system that exists only in memory. Unlike unionfs, memfs does not support combining multiple file systems but is often used in conjunction with unionfs to provide in-memory file system capabilities.

mock-fs

mock-fs allows you to mock the file system in Node.js, making it useful for testing purposes. It provides a way to create a virtual file system with a specified structure. While it does not support combining multiple file systems like unionfs, it is useful for creating isolated file system environments for testing.

README

unionfs

Creates a union of multiple fs file systems.

npm install --save unionfs

This module allows you to use multiple objects that have file system fs API at the same time.

import { ufs } from 'unionfs';
import { fs as fs1 } from 'memfs';
import * as fs2 from 'fs';

ufs.use(fs1).use(fs2);

ufs.readFileSync(/* ... */);

Use this module with memfs and linkfs. memfs allows you to create virtual in-memory file system. linkfs allows you to redirect fs paths.

You can also use other fs-like objects.

import * as fs from 'fs';
import { Volume } from 'memfs';
import * as MemoryFileSystem from 'memory-fs';
import { ufs } from 'unionfs';

const vol1 = Volume.fromJSON({ '/memfs-1': '1' });
const vol2 = Volume.fromJSON({ '/memfs-2': '2' });

const memoryFs = new MemoryFileSystem();
memoryFs.writeFileSync('/memory-fs', '3');

ufs.use(fs).use(vol1).use(vol2).use(memoryFs);

console.log(ufs.readFileSync('/memfs-1', 'utf8')); // 1
console.log(ufs.readFileSync('/memfs-2', 'utf8')); // 2
console.log(ufs.readFileSync('/memory-fs', 'utf8')); // 3

You can create a Union instance manually:

import { Union } from 'unionfs';

var ufs1 = new Union();
ufs1.use(fs).use(vol);

var ufs2 = new Union();
ufs2.use(fs).use(/*...*/);

License

Unlicense - public domain.

Changelog

4.5.4 (2024-03-19)

Bug Fixes

• readdir and readdirSync failing on valid empty directory if another fs fails (#787) (dab090e)