mem-fs

What is mem-fs?

The mem-fs npm package provides an in-memory file system that allows developers to perform file operations without affecting the actual file system. This is particularly useful for testing, prototyping, and scenarios where temporary file manipulation is needed.

What are mem-fs's main functionalities?

Creating a File Store

This feature allows you to create an in-memory file store and an editor instance to interact with it. The `mem-fs` package is used to create the store, and `mem-fs-editor` is used to create an editor instance that can manipulate the store.

const memFs = require('mem-fs');
const editor = require('mem-fs-editor');
const store = memFs.create();
const fs = editor.create(store);

Writing Files

This feature allows you to write files to the in-memory file system. The `write` method is used to specify the file path and content, and the `commit` method is used to apply the changes.

fs.write('path/to/file.txt', 'Hello, world!');
fs.commit(() => {
  console.log('File written!');
});

Reading Files

This feature allows you to read files from the in-memory file system. The `read` method is used to specify the file path and retrieve its content.

const content = fs.read('path/to/file.txt');
console.log(content);

Deleting Files

This feature allows you to delete files from the in-memory file system. The `delete` method is used to specify the file path, and the `commit` method is used to apply the changes.

fs.delete('path/to/file.txt');
fs.commit(() => {
  console.log('File deleted!');
});

Other packages similar to mem-fs

mock-fs

The mock-fs package provides a way to mock the file system in Node.js. It allows you to create a virtual file system for testing purposes. Unlike mem-fs, which focuses on in-memory file operations, mock-fs is designed to mock the entire file system, making it suitable for more comprehensive testing scenarios.

fs-extra

The fs-extra package extends the native Node.js file system module with additional methods and features. While it does not provide an in-memory file system, it offers a wide range of file manipulation utilities that can be useful for various file operations. It is more focused on enhancing the existing file system capabilities rather than providing an in-memory solution.

vinyl-fs

The vinyl-fs package is a file system adapter for the Vinyl virtual file format, commonly used in the Gulp build system. It allows you to work with files in a stream-based manner. While it does not provide an in-memory file system, it offers a flexible way to handle file operations in build processes.

README

mem-fs

Simple in-memory vinyl file store.

Usage

Loading a file

You access a file using store#get() method. If the file is in memory, it will be used. Otherwise, we'll load the file from the file-system.

import { create } from 'mem-fs';

const store = create();
store.get('/test/file.txt');

When trying to load a file we cannot read from disk, an empty Vinyl file will be returned. The contents of this file will be set to null.

Trying to get a directory or any invalid files will also return an empty Vinyl file pointer.

Adding/updating a file

You update file references by using store#add() method. This method take a vinyl file object as parameter.

import File from 'vinyl';
import { create } from 'mem-fs';

const coffeeFile = new File({
  cwd: '/',
  base: '/test/',
  path: '/test/file.coffee',
  contents: new Buffer('test = 123'),
});

const store = create();
store.add(coffeeFile);

Iterating over the file system

Using store#each(cb(file, index)), you can iterate over every file stored in the file system.

Get all files

Using store#all(), you can get every file stored in the file system.

Check existence in the file system

Using store#existsInMemory(), you can check if the file already exists in the file system without loading it from disk.

Stream every file stored in the file system

Using store#stream(), you can create a stream with every file stored in the file system.

Pass stored files through a pipeline

store#pipeline() generates a new map with yielded files in transforms. If no transform is passed, files references are updated.