npm / memfs

memfs

What changed in memfs 4, from its official release notes, upgrade guides and advisories. Sources checked 2026-10-18.

5 breaking1 security1 deprecations12 new APIs and options2 performance6 behavior and defaults1 tooling15 fixes and other

See which of these apply to your code, ranked, in your agent:

npx @unstale/cli init

memfs 443 changes

Symlink resolution is now bounded at 40 and uses an improved algorithm for all open calls.
4.70.0release notes
.unlink() no longer deletes empty directories.
4.68.1release notes
Removed tslib from peerDependencies, changing the package's peer dependency requirements.
4.66.0release notes
Relative paths are no longer allowed during snapshot restoration.
4.57.7release notes
toTreeSync() sorts files and folders in its output.
4.51.0release notes

Negative truncate lengths are clamped to zero, preventing an uninitialized-memory leak.
4.57.8release notes

Adds the deprecated Dirent.path property with a deprecation notice.
4.52.0release notes

The synchronous FSA worker timeout can now be configured.
4.80.0release notes
A Node-compatible cp module is implemented, allowing developers to use cp functionality with memfs.
4.78.0release notes
Adds glob support to memfs.
4.77.0release notes
Adds support for file birth time.
4.68.0release notes
FsaNodeFs now supports the recursive flag.
4.65.0release notes
Adds a Node-to-FSA watcher bridge.
4.63.0release notes
A FileSystemObserver implementation is available.
4.61.0release notes
Event emission was added to fs-core.
4.58.0release notes
A custom process implementation can now be injected for better testability.
4.57.0release notes
A Result type is implemented, and error handling for exists methods is improved.
4.53.0release notes
Adds the Dirent.parentPath property.
4.52.0release notes
Adds disposable methods to Dir.
4.52.0release notes

The read/write path was improved, which may affect performance when using memfs.
4.73.0release notes
Improves Node buffer allocation and management to prevent O(n^2) overhead.
4.50.0release notes

Improvements to Dir change its behavior for developers using the API.
4.76.0release notes
Improvements to .opendir() change its behavior for developers using the API.
4.76.0release notes
Flags validation errors are improved, making validation failures clearer to developers.
4.74.0release notes
Error normalization is more Node.js-like, affecting the errors developers receive.
4.71.0release notes
The git-fsa directory handle is now persisted.
4.67.0release notes
FSA writable handles now have locking.
4.54.0release notes

Published sourcemaps now embed sources, which can make source content available when debugging builds.
4.66.1release notes

Improves FS(A) error handling.
4.79.0release notes
Returns the correct shape from queryPermission.
4.78.1release notes
Error formatting and normalization are improved.
4.75.0release notes
Relative streams are resolved from the virtual cwd.
4.72.2release notes
BYOB file stream reads now finish at EOF.
4.72.1release notes
Path validation errors are improved, making invalid paths easier to diagnose.
4.72.0release notes
Directory iteration now matches Node's lifecycle.
4.71.1release notes
Improved support for the O_NOFOLLOW flag.
4.69.0release notes
O_APPEND behavior is aligned with Linux.
4.68.2release notes
Fixes handling of drive letters in file URLs.
4.66.0release notes
Enabled cpSync in fsSynchronousApiList.
4.57.3release notes
Enabled statfsSync in fsSynchronousApiList.
4.57.3release notes
Symlinks are now followed when checking for the executable flag.
4.57.2release notes
Fixes EBADF when calling fileHandle.close after streaming via pipeline.
4.57.1release notes
Leading ./ is normalized in relative glob patterns.
4.56.11release notes