ZenFS is a file system that emulates the NodeJS filesystem API.

It works using a system of backends, which are used by ZenFS to store and retrieve data. ZenFS can also integrate with other tools.

ZenFS is a fork of BrowserFS.

ZenFS is modular and extensible. The core includes a few built-in backends:

• InMemory: Stores files in-memory. This is cleared when the runtime ends (e.g. a user navigating away from a web page or a Node process exiting)
• Overlay: Use read-only file system as read-write by overlaying a writable file system on top of it.
• AsyncMirror: Use an asynchronous backend synchronously. This is very helpful for asynchronous backends

ZenFS supports a number of other backends. Many are provided as seperate packages under @zenfs. More backends can be defined by separate libraries by extending the FileSystem class and/or providing a Backend object.

For more information, see the docs.

npm install @zenfs/core

import fs from '@zenfs/core'; // You can also use the named export, `fs`

fs.writeFileSync('/test.txt', 'Cool, I can do this in any JS environment (including browsers)!');

const contents = fs.readFileSync('/test.txt', 'utf-8');
console.log(contents);

A single InMemory backend is created by default, mounted on /.

You can configure ZenFS to use a different backend and mount multiple backends. It is strongly recommended to do so using the configure function.

You can use multiple backends by passing an object to configure which maps paths to file systems.

The following example mounts a zip file to /zip, in-memory storage to /tmp, and IndexedDB to /home. Note that / has the default in-memory backend.

import { configure, InMemory } from '@zenfs/core';
import { IndexedDB } from '@zenfs/dom';
import { Zip } from '@zenfs/zip';

const zipData = await (await fetch('mydata.zip')).arrayBuffer();

await configure({
	'/mnt/zip': { backend: Zip, zipData },
	'/tmp': InMemory,
	'/home': IndexedDB,
};

Here is an example that mounts the Storage backend from @zenfs/dom on /:

import { configure, fs } from '@zenfs/core';
import { Storage } from '@zenfs/dom';

await configure({ backend: Storage });

if (!fs.existsSync('/test.txt')) {
	fs.writeFileSync('/test.txt', 'This will persist across reloads!');
}

const contents = fs.readFileSync('/test.txt', 'utf-8');
console.log(contents);

The FS promises API is exposed as promises.

import { configure, promises } from '@zenfs/core';
import { IndexedDB } from '@zenfs/dom';

await configure({ '/': IndexedDB });

const exists = await promises.exists('/myfile.txt');
if (!exists) {
	await promises.write('/myfile.txt', 'Lots of persistant data');
}

You may have noticed that attempting to use a synchronous function on an asynchronous backend (e.g. IndexedDB) results in a "not supplied" error (ENOTSUP). If you would like to use an asynchronous backend synchronously you need to wrap it in an AsyncMirror:

import { configure, fs, AsyncMirror, InMemory } from '@zenfs/core';
import { IndexedDB } from '@zenfs/dom';

await configure({
	'/': {
		backend: AsyncMirror,
		sync: InMemory,
		async: IndexedDB,
	},
});

fs.writeFileSync('/persistant.txt', 'My persistant data');

If you would like to create backends without configure (e.g. to do something dynamic at runtime), you may do so by importing the backend and calling createBackend with it.

You can then mount and unmount the backend instance by using mount and umount.

import { configure, createBackend, InMemory } from '@zenfs/core';
import { IndexedDB  } from '@zenfs/dom';
import { Zip } from '@zenfs/zip';

await configure({
	'/tmp': InMemory,
	'/home': IndexedDB,
};

fs.mkdirSync('/mnt');

const res = await fetch('mydata.zip');
const zipFs = await createBackend(Zip, { zipData: await res.arrayBuffer() });
fs.mount('/mnt/zip', zipFs);

// do stuff with the mounted zip

fs.umount('/mnt/zip'); // finished using the zip

ZenFS exports a drop-in for Node's fs module (up to the version of @types/node in package.json), so you can use it for your bundler of preference using the default export.

• Make sure you have Node and NPM installed. You must have Node v18 or newer.
• Install dependencies with npm install
• Build using npm run build
• You can find the built code in dist.

Run unit tests with npm test.