In-Memory File System

memfs is a JavaScript library that provides an in-memory file system, designed to be highly compatible with Node.js's native `fs` module API and the browser's File System (Access) API. It serves as a robust tool for testing, mocking file system operations, and creating isolated virtual environments across both Node.js and modern browser runtimes. The current stable version is `4.57.2`. The project exhibits an active release cadence, with frequent patch and minor updates, as indicated by the rapid succession of releases between January and April 2026. Its key differentiators include comprehensive dual API compatibility, built-in TypeScript support, and helpful utilities like directory snapshots, making it a versatile solution for cross-environment file system virtualization.