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memfs (3.5.3)

Published 2026-02-24 14:01:15 +00:00 by atheaadmin

Installation

Setup this registry in your project .npmrc file:

registry=

To install the package using npm, run the following command:

npm install memfs@3.5.3

or add it to the package.json file:

"memfs": "3.5.3"

For more information on the npm registry, see the documentation.

About this package

memfs

In-memory file-system with Node's fs API.

• Node's fs API implemented, see old API Status, missing list, missing opendir
• Stores files in memory, in Buffers
• Throws sameish* errors as Node.js
• Has concept of i-nodes
• Implements hard links
• Implements soft links (aka symlinks, symbolic links)
• Permissions may* be implemented in the future
• Can be used in browser, see memfs-webpack

Install

npm install --save memfs

Usage

import { fs } from 'memfs';

fs.writeFileSync('/hello.txt', 'World!');
fs.readFileSync('/hello.txt', 'utf8'); // World!

Create a file system from a plain JSON:

import { fs, vol } from 'memfs';

const json = {
  './README.md': '1',
  './src/index.js': '2',
  './node_modules/debug/index.js': '3',
};
vol.fromJSON(json, '/app');

fs.readFileSync('/app/README.md', 'utf8'); // 1
vol.readFileSync('/app/src/index.js', 'utf8'); // 2

Export to JSON:

vol.writeFileSync('/script.sh', 'sudo rm -rf *');
vol.toJSON(); // {"/script.sh": "sudo rm -rf *"}

Use it for testing:

vol.writeFileSync('/foo', 'bar');
expect(vol.toJSON()).toEqual({ '/foo': 'bar' });

Create as many filesystem volumes as you need:

import { Volume } from 'memfs';

const vol = Volume.fromJSON({ '/foo': 'bar' });
vol.readFileSync('/foo'); // bar

const vol2 = Volume.fromJSON({ '/foo': 'bar 2' });
vol2.readFileSync('/foo'); // bar 2

Use memfs together with unionfs to create one filesystem from your in-memory volumes and the real disk filesystem:

import * as fs from 'fs';
import { ufs } from 'unionfs';

ufs.use(fs).use(vol);

ufs.readFileSync('/foo'); // bar

Use fs-monkey to monkey-patch Node's require function:

import { patchRequire } from 'fs-monkey';

vol.writeFileSync('/index.js', 'console.log("hi world")');
patchRequire(vol);
require('/index'); // hi world

Docs

• Reference
• Relative paths
• API status
• Dependencies

See also

• spyfs - spies on filesystem actions
• unionfs - creates a union of multiple filesystem volumes
• linkfs - redirects filesystem paths
• fs-monkey - monkey-patches Node's fs module and require function
• libfs - real filesystem (that executes UNIX system calls) implemented in JavaScript

License

Unlicense - public domain.

Dependencies

Dependencies

ID	Version
fs-monkey	^1.0.4

Development Dependencies

ID	Version
@semantic-release/changelog	^6.0.1
@semantic-release/git	^10.0.1
@semantic-release/npm	^9.0.1
@types/jest	^27.5.2
@types/node	^10.17.60
husky	^8.0.1
jest	^28.1.1
prettier	^2.7.1
pretty-quick	^3.1.3
rimraf	^3.0.2
semantic-release	^19.0.3
ts-jest	^28.0.5
ts-node	^10.8.1
tslint	^5.20.1
tslint-config-common	^1.6.0
typescript	^4.7.4

Keywords

fs filesystem fs.js memory-fs memfs file file system mount memory in-memory virtual test testing mock

Details

npm

2026-02-24 14:01:15 +00:00

1

Project Site

Unlicense

latest

38 KiB

Assets (1)

memfs-3.5.3.tgz 38 KiB

Versions (1) View all

3.5.3 2026-02-24