Registry / testing / memory-fs

memory-fs

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library0.41.0jsnpmunverified

memory-fs provides a simple, synchronous and asynchronous, in-memory filesystem abstraction, designed to hold data entirely within a JavaScript object. It mirrors a subset of the Node.js `fs` module API, making it suitable for scenarios where persistent disk I/O is undesirable or impractical, such as build tools, bundlers, and testing environments. The current stable version, 0.5.0, was released in 2017. While not actively developing new features, it is a critical, stable dependency for projects like Webpack, which relies on it for fast, transient asset compilation. Its primary differentiator is its complete in-memory operation and direct API compatibility with many standard `fs` methods, offering a performant alternative to disk-based operations for temporary file storage.

testing
npm install memory-fs
github ↗package ↗
INSTALL
IMPORT
SIG · MEMORY-FS
M
memory-fs
testingjavascriptv0.41.0
Install
—
Import
—
Disk
—
Pass rate
0/ 6
Env Coverage0 / 6
glibc
18–22
musl
18–22
Install & Compatibility
Where this runs
tested against v? · npm install
Install × environment matrix
Each cell = how many times install + import succeeded across repeated harness runs. Partial = flaky.
glibc = Debian/Ubuntu slim · musl = Alpine Linux
musl
node 18–226 runs
build_error
glibc
node 18–226 runs
build_error
Code
Verified usage

Verified import paths — ran on the pinned version, not inferred.

MemoryFileSystem
✓ const MemoryFileSystem = require('memory-fs');
✗ import MemoryFileSystem from 'memory-fs';
This package is CommonJS-only. Attempting to use ES module import syntax will result in errors.
fsInstance
✓ const fs = new MemoryFileSystem();
✗ const fs = require('memory-fs'); // Does not return an instance
The `require` call returns the constructor function, which must be instantiated to get a functional filesystem object.

Demonstrates basic synchronous and asynchronous file operations (create, write, read, delete, list, stat) using the `memory-fs` API.

const MemoryFileSystem = require('memory-fs'); const fs = new MemoryFileSystem(); // Optionally pass an initial JavaScript object, e.g., { 'src': { 'main.js': 'console.log("Hello");' } } // Create directories fs.mkdirpSync("/a/test/dir"); console.log('Created /a/test/dir'); // Write and read a file const filePath = "/a/test/dir/file.txt"; fs.writeFileSync(filePath, "Hello World from memory-fs"); console.log(`Content of ${filePath}: ${fs.readFileSync(filePath, 'utf8')}`); // Async file unlink fs.unlink(filePath, function(err) { if (err) { console.error(`Error unlinking file: ${err.message}`); return; } console.log(`${filePath} unlinked successfully.`); }); // List directory contents console.log(`Contents of /a/test: ${fs.readdirSync("/a/test")}`); // Get file/directory stats const stats = fs.statSync("/a/test/dir"); console.log(`/a/test/dir is a directory: ${stats.isDirectory()}`); // Clean up directory fs.rmdirSync("/a/test/dir"); console.log('Removed /a/test/dir');
Debug
Known issues
breakingThe `engines` field in package.json restricts compatible Node.js versions. Specifically, it requires Node.js `>=4.3.0 <5.0.0 || >=5.10`. Using unsupported Node.js versions may lead to unexpected behavior or installation failures.
fix
Ensure your Node.js environment matches the specified engine compatibility range or use a tool like `nvm` to manage Node.js versions.
affects: >=0.1.0
gotchamemory-fs provides only a subset of the standard Node.js `fs` module API. While it implements common methods like `readFile`, `writeFile`, `readdir`, and `stat`, many advanced or less frequently used `fs` methods are not available.
fix
Always check the `memory-fs` documentation or source code for method availability. Do not assume full `fs` compatibility.
affects: >=0.1.0
gotchaThis package is CommonJS-only and does not natively support ES module `import` syntax. Attempting to use `import` will result in a runtime error.
fix
Use CommonJS `require()` syntax: `const MemoryFileSystem = require('memory-fs');`.
affects: >=0.1.0
gotchaUnlike the native `fs` module, `memory-fs` requires explicit instantiation via `new MemoryFileSystem()`. Importing the package directly does not yield a functional filesystem object.
fix
After `require('memory-fs')`, always call `new MemoryFileSystem()` to get an instance, e.g., `const fs = new MemoryFileSystem();`.
affects: >=0.1.0
Errors
Common errors & fixes
TypeError: MemoryFileSystem is not a constructor
Attempting to call `new` on the result of `require('memory-fs')` when the variable was incorrectly reassigned or handled.
fix
Ensure `const MemoryFileSystem = require('memory-fs');` directly assigns the constructor to `MemoryFileSystem` and then `const fs = new MemoryFileSystem();` is called.
ReferenceError: require is not defined in ES module scope
Trying to use `require` in a file or project configured for ES modules (`"type": "module"` in package.json).
fix
This package is CommonJS-only. For projects using ES modules, you might need to use a bundler (like Webpack) that handles CommonJS dependencies, or restructure your code to load this module in a CommonJS context.
TypeError: fs.someMethod is not a function
Attempting to call an `fs` module method that is not implemented by `memory-fs` (e.g., `fs.watch`, `fs.createReadStream`).
fix
Verify that the specific `fs` method you need is supported by `memory-fs`. If not, you may need to reconsider its use for that particular operation or find an alternative library.
Upgrade
Version history
0.41.0latest on npm
Audit
Dependencies

No dependency data recorded yet.

Agent activity
2 hits · last 30 days
node
2
Resources
githubhttps://github.com/webpack/memory-fs ↗
packagehttps://www.npmjs.com/package/memory-fs ↗
memory-fs — npm install memory-fs · libregistry