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npm · #1277 most downloaded on npm
In-memory file-system with Node's fs API.
Last release today
17 Sep 2026
Ships fairly regularly
a new release about every 2 weeks
Nearly every release is documented
notes for 57 of the last 60 stable releases
2 versions withdrawn
withdrawn after publishing
11 years old
265 releases · first in 2015
inline fs.ts types to remove node:fs dependency
One column per quarter.
Use cross-platform dirname instead of posix.dirname (7a51ac3), closes #1193
.openAsBlob() for FsaNodeFs (26068e8)CoreFileSystemObserver implementation and restructure fsa() helper (117b7c5)IFileSystemChangeRecord interface (868b763)IFileSystemObserver interface (d581d8c)FanOut for Link reactivity (2aec586)FanOut for Node events (95ef10a)re-export all Node.js native packages
🎸 implement .openAsBlob() for FsaNodeFs
update TypeScript and related packages to latest versions
update Node.js types and add node: prefix to imports
🎸 add scaffold for CoreFileSystemObserver implementation and restructure fsa() helper
CoreFileSystemObserver implementation and restructure fsa() helper (117b7c5)IFileSystemChangeRecord interface (868b763)IFileSystemObserver interface (d581d8c)FanOut for Link reactivity (2aec586)FanOut for Node events (95ef10a)prevent readFile from updating ctime when only accessing files
correct permission check logic for readonly files in copyFile operations
## 4.38.1 (2025-08-24) ### Bug Fixes * 🐛 use glob-to-regex library
handle chmod 0 permissions in existsSync and access methods
ensure FLAG enum is properly exported for compatibility with Node.js fs.open
implement async queryPermission with FSA context mode checks
🐛 remove CRUD and CAS fs implementations
🐛 check for buffer size when stream reading
🐛 correctly write at offset in FS adapter
# 4.36.0 (2025-08-03) ### Features * 🎸 harden WritableStream usage
directory timestamp handling - correctly distinguish access vs modification operations
add ENOTDIR error for files accessed with trailing slash
correct ENOTDIR vs ENOENT error handling after symlink resolution
remove setTimeout to capture immediate file events in watched directories
ensure glob APIs use consistent posix paths on all platforms
improve FileHandle.readableWebStream() with proper locking and autoClose support
add missing name check in FsaNodeSyncWorker.getFileOrDir for root directory
remove implemented APIs from missing-apis tests
add missing Node.js fs APIs with proper TypeScript types and stubs
correct writevSync return type to number per Node.js documentation
# 4.28.0 (2025-07-31) ### Features * 🎸 export fsa() factory
resolve security regex issue and constructor bug in FSA classes
revert yarn.lock changes and fix import paths in moved test files
remove await in loop for toSnapshot
promises.watch (45a6171)🐛 correct imports graph to fix Windows path resolution
refactor core classes to separate files
# 4.23.0 (2025-07-27) ### Features * add promises.watch
fs.createReadStream throwing ERR_OUT_OF_RANGE with start parameter
add realpath.native and its sync variant
improve Dir class, align better with Node.js
track internal position in FileHandle
FileHandle implementation (4b39403)improve FileHandle implementation
improve cross-platform path validation in cp operations to prevent Windows infinite recursion
# 4.18.0 (2025-07-25) ### Features * add missing opendir methods
use promises rather than setImmediate so that I/O is executed within the current task stack
export Volume class directly rather than as a const
# 4.17.0 (2025-01-09) ### Features * allow setting rdev on node
support UInt8Array in place of Buffer
## 4.15.4 (2025-01-09) ### Bug Fixes * remove debugger statement
allow setting custom file types beyond S_IFREG and S_IFDIR
don't fail on closing fd after reset has been called
resolve relative symlinks to the current directory (#1079) (63e3873), closes #725
implement createReadStream and createWriteStream on FileHandle (#1076) (c413df5), closes #1063
accept passing a FileHandle to createReadStream and createWriteStream
support stream as source in promises version of writeFile
# 4.13.0 (2024-10-07) ### Features * implement lutimes
# 4.12.0 (2024-09-19) ### Features * improve permissions support
🐛 declare ReadableStream global type
volume implementation of .opendir() method
🎸 add IReadableWebStreamOptions type
ensure files in subdirectories are returned as buffers when calling toJSON with asBuffer
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