# @jsonjoy.com/fs-core > Core filesystem primitives: Node, Link, File, Superblock Latest version **4.79.0** (published 2026-09-22) · Apache-2.0 license · 0 weekly downloads ## Install ```sh npm install @jsonjoy.com/fs-core pnpm add @jsonjoy.com/fs-core yarn add @jsonjoy.com/fs-core bun add @jsonjoy.com/fs-core ``` ## Health **Score 70/100 (B)** — status: active. Positive: has types; no vulnerabilities; has provenance; recently updated; high maintenance score; high quality score. Warnings: low downloads; no esm support. ## Facts | | | |---|---| | Version | 4.79.0 | | Published | 2026-09-22 | | First published | 2026-01-19 | | Weekly downloads | 0 | | License | Apache-2.0 | | TypeScript types | bundled | | Module format | CommonJS | | Node | >=10.0 | | Dependencies | 3 | | Unpacked size | 240.3 KB | | Known vulnerabilities | 0 | | Install scripts | no | | Provenance | attested (GitHub Actions) | | GitHub stars | 2091 | | Author | streamich | | Maintainers | json-joy-team, streamich | | Keywords | node, fs, filesystem, inode, link, file, superblock, virtual, memory | ## Links - npm: https://www.npmjs.com/package/@jsonjoy.com/fs-core - Repository: https://github.com/streamich/memfs - Homepage: https://github.com/streamich/memfs/tree/master/packages/fs-core - Issues: https://github.com/streamich/memfs/issues - Funding: https://github.com/sponsors/streamich - npm.io page: https://npm.io/package/@jsonjoy.com/fs-core ## Dependencies (3) - [thingies](https://npm.io/package/thingies.md) ^2.5.0 - [@jsonjoy.com/fs-node-utils](https://npm.io/package/@jsonjoy.com/fs-node-utils.md) 4.79.0 - [@jsonjoy.com/fs-node-builtins](https://npm.io/package/@jsonjoy.com/fs-node-builtins.md) 4.79.0 ## Alternatives - [unionfs](https://npm.io/package/unionfs.md) — 2.2M weekly downloads - [path-starts-with](https://npm.io/package/path-starts-with.md) — 35.9K weekly downloads - [redzip](https://npm.io/package/redzip.md) — 1.2K weekly downloads - [vscode-anymatch](https://npm.io/package/vscode-anymatch.md) — 848 weekly downloads - [@ledgerhq/coin-filecoin](https://npm.io/package/@ledgerhq/coin-filecoin.md) — 793 weekly downloads ## Recent versions - 4.79.0 (latest) — 2026-09-22 - 4.78.1 — 2026-09-17 - 4.78.0 — 2026-09-13 - 4.77.0 — 2026-09-13 - 4.76.0 — 2026-09-12 - 4.75.0 — 2026-09-11 - 4.74.0 — 2026-09-10 - 4.73.0 — 2026-09-10 - 4.72.2 — 2026-09-10 - 4.72.1 — 2026-09-09 - 4.72.0 — 2026-09-09 - 4.71.1 — 2026-09-09 - 4.71.0 — 2026-09-04 - 4.70.0 — 2026-09-04 - 4.69.1 — 2026-09-02 - … 33 more at https://npm.io/package/@jsonjoy.com/fs-core/versions ## README # memfs [![][npm-badge]][npm-url] [npm-url]: https://www.npmjs.com/package/memfs [npm-badge]: https://img.shields.io/npm/v/memfs.svg JavaScript file system utilities for Node.js and browser. Implementation of in-memory [Node.js `fs` module API](https://nodejs.org/api/fs.html) and in-memory [browser File System API](https://developer.mozilla.org/en-US/docs/Web/API/File_System_API), as well as adapters from `fs` module to File Sytem API and from File Sytem API to `fs` module. ## Install ```shell npm i memfs ``` ## Resources - [In-memory Node.js `fs` API](./docs/node/index.md) - [In-memory browser File System (Access) API](./docs/fsa/fsa.md) - [`fs` to File System (Access) API adapter](./docs/fsa/fs-to-fsa.md) - [File System (Access) API to `fs` adapter](./docs/fsa/fsa-to-fs.md) - [Directory `snapshot` utility](./docs/snapshot/index.md) - [`print` directory tree to terminal](./docs/print/index.md) - [Code reference](https://streamich.github.io/memfs/) - [Test coverage](https://streamich.github.io/memfs/coverage/lcov-report/) ## Watching All file-watching APIs are implemented on both sides of the `fs` and File System API divide: | Feature | Package | Notes | | -------------------------------------------------------------------------- | -------------------------------------------------------- | --------------------------------------------------------------------------------------- | | `fs.watch` — `recursive`, `encoding`, `signal`, `throwIfNoEntry`, `ignore` | [`@jsonjoy.com/fs-node`](packages/fs-node) | `'error'`/`'close'` events, `ref()`/`unref()` | | `fs.watchFile` / `fs.unwatchFile` | [`@jsonjoy.com/fs-node`](packages/fs-node) | polling, `bigint`, Node's reappearance semantics | | `fs.promises.watch` async iterator | [`@jsonjoy.com/fs-node`](packages/fs-node) | `maxQueue`, `overflow`, `AbortError` on abort | | [`FileSystemObserver`][observer] | [`@jsonjoy.com/fs-fsa`](packages/fs-fsa) | deterministic OPFS profile: precise records, real `"moved"` records, microtask batching | | `fs.watch`/`fs.watchFile` over a real FSA directory | [`@jsonjoy.com/fs-fsa-to-node`](packages/fs-fsa-to-node) | works over OPFS in Chrome 133+ via the native observer | | `FileSystemObserver` over any `fs` | [`@jsonjoy.com/fs-node-to-fsa`](packages/fs-node-to-fsa) | best-effort profile: renames stat-classified, no `"moved"` records | Intentional divergences from real watchers (the in-memory backend is deterministic, so platform unreliability is not emulated): - Paths are watched semantically rather than by inode: after delete-and-recreate, memfs reports events for the recreated entry, while a real POSIX watcher keeps watching the dead inode. - Exactly one event per logical operation — no platform duplicate events. - `filename` is never `null`. - The Node-style `FSWatcher` delivers events synchronously inside the mutating operation, whereas real Node defers to the event loop; the `FileSystemObserver` batches per microtask, as the spec requires. [observer]: https://developer.mozilla.org/en-US/docs/Web/API/FileSystemObserver ## Demos - [Git in browser, which writes to a real folder](demo/git-fsa/README.md) - [Git in browser, which writes to OPFS file system](demo/git-opfs/README.md) - [Git on in-memory file system](demo/git/README.md) - [`fs` in browser, creates a `.tar` file in real folder](demo/fsa-to-node-zipfile/README.md) - [`fs` in browser, synchronous API, writes to real folder](demo/fsa-to-node-sync-tests/README.md) ## See also - [`unionfs`][unionfs] - creates a union of multiple filesystem volumes - [`fs-monkey`][fs-monkey] - monkey-patches Node's `fs` module and `require` function - [`linkfs`][linkfs] - redirects filesystem paths - [`spyfs`][spyfs] - spies on filesystem actions [unionfs]: https://github.com/streamich/unionfs [fs-monkey]: https://github.com/streamich/fs-monkey [linkfs]: https://github.com/streamich/linkfs [spyfs]: https://github.com/streamich/spyfs ## License Apache 2.0 --- _Source: https://npm.io/package/@jsonjoy.com/fs-core · Machine-readable twin of the npm.io package page. Health data is recomputed on every publish._