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Reference

vol vs fs

This package exports vol and fs objects which both can be used for filesystem operations but are slightly different.

import { vol, fs } from 'memfs';

vol is an instance of Volume constructor, it is the default volume created for your convenience. fs is an fs-like object created from vol using createFsFromVolume(vol), see reference below.

All contents of the fs object are also exported individually, so you can use memfs just like you would use the fs module:

import { readFileSync, F_OK, ReadStream } from 'memfs';

Volume Constructor

Volume is a constructor function for creating new volumes:

import { Volume } from 'memfs';
const vol = new Volume();

Volume implements all Node's filesystem methods:

vol.writeFileSync('/foo', 'bar');

But it does not hold constants and its methods are not bound to vol:

vol.F_OK; // undefined

A new volume can be create using the Volume.fromJSON convenience method:

const vol = Volume.fromJSON({
  '/app/index.js': '...',
  '/app/package.json': '...',
});

It is just a shorthand for vol.fromJSON, see below.

Volume instance vol

vol.fromJSON(json[, cwd])

Adds files from a flat json object to the volume vol. The cwd argument is optional and is used to compute absolute file paths, if a file path is given in a relative form.

Note: To remove all existing files, use vol.reset() method.

vol.fromJSON(
  {
    './index.js': '...',
    './package.json': '...',
  },
  '/app',
);

vol.mountSync(cwd, json)

Legacy method, which is just an alias for vol.fromJSON.

vol.toJSON([paths[, json[, isRelative]]])

Exports the whole contents of the volume recursively to a flat JSON object.

paths is an optional argument that specifies one or more paths to be exported. If this argument is omitted, the whole volume is exported. paths can be an array of paths. A path can be a string, Buffer or an URL object.

json is an optional object parameter which will be populated with the exported files.

isRelative is boolean that specifies if returned paths should be relative.

Note: JSON contains only files, empty folders will be absent.

vol.reset()

Removes all files from the volume.

vol.fromJSON({ '/index.js': '...' });
vol.toJSON(); // {'/index.js': '...' }
vol.reset();
vol.toJSON(); // {}

vol.mkdirp(path[, mode], callback)

DEPRECATED: This method will be removed in next major release. Use vol.mkdir(..., {recursive: true}, callback) instead.

Legacy interface, which now uses the recursive option of vol.mkdir.

Creates a directory tree recursively. path specifies a directory to create and can be a string, Buffer, or an URL object. callback is called on completion and may receive only one argument - an Error object.

vol.mkdirpSync(path[, mode])

DEPRECATED: This method will be removed in next major release. Use vol.mkdirSync(..., {recursive: true}) instead.

Legacy interface, which now uses the recursive option of vol.mkdirSync.

A synchronous version of vol.mkdirp(). This method throws.

createFsFromVolume(vol)

Returns an fs-like object created from a Volume instance vol.

import { createFsFromVolume, Volume } from 'memfs';

const vol = new Volume();
const fs = createFsFromVolume(vol);

The idea behind the fs-like object is to make it identical to the one you get from require('fs'). Here are some things this function does:

  • Binds all methods, so you can do:
const { createFileSync, readFileSync } = fs;
  • Adds constants fs.constants, fs.F_OK, etc.