opfs-mock

In-memory implementation of the origin private file system. Its main utility is for testing OPFS-dependent code in Node.js. It's tested on Node.js versions 20-25.

Installation

npm install -save-dev opfs-mock

Limitations

• opfs-mock requires Node.js v20.0.0 or higher. It can work on Node v18.0.0 with either --experimental-fetch flag enabled or a global File polyfill.

• jsdom testing environment is missing File.prototype.text() method, which is required for reading opfs files. Ensure your opfs-dependant tests are ran in node or happy-dom environment.

Usage

It replicates the behavior of origin private file system, except data is not persisted to disk.

The easiest way to use it is to import opfs-mock, which will polyfill OPFS API to global scope.

import "opfs-mock";

Alternatively, you can explicitly import storageFactory:

import { storageFactory } from "opfs-mock";

test('Your test', async () => {
  const storage = await storageFactory();
  const root = await storage.getDirectory();
  const directoryHandle = await root.getFileHandle('test-file.txt', { create: true });
  // rest of your test
});

storageFactory has quota and usage values set to 1024 ** 3 (1 GB) and 0 respectively. When calling storage.estimate(), usage is dynamically calculated by summing the predefined usage value and any additional computed storage consumption. In case you need specific values, you can pass both as arguments to storageFactory.

import { storageFactory } from "opfs-mock";

test('Your test', async () => {
  const storage = await storageFactory({ quota: 1_000_000, usage: 1_000 });
  const root = await storage.getDirectory();
  const directoryHandle = await root.getFileHandle('test-file.txt', { create: true });
  // rest of your test
});

Vitest

To use opfs-mock in a single Vitest test suite, require opfs-mock at the beginning of the test file, as described above.

To use it on all Vitest tests without having to include it in each file, add the auto setup script to the test.setupFiles in your Vite config:

// vite.config.ts

import { defineConfig as defineViteConfig, mergeConfig } from 'vite';
import { defineConfig as defineVitestConfig } from 'vitest/config';

const viteConfig = defineViteConfig({
  ...
});

const vitestConfig = defineVitestConfig({
  test: {
    setupFiles: ['opfs-mock'],
  },
});

export default mergeConfig(viteConfig, vitestConfig);

Alternatively you can create a new setup file which then imports this module.

// vitest-setup.ts

import "opfs-mock";

Add that file to your test.setupFiles array:

// vite.config.ts

import { defineConfig as defineViteConfig, mergeConfig } from 'vite';
import { defineConfig as defineVitestConfig } from 'vitest/config';

const viteConfig = defineViteConfig({
  ...
});

const vitestConfig = defineVitestConfig({
  test: {
    setupFiles: ['vitest-setup.ts'],
  },
});

export default mergeConfig(viteConfig, vitestConfig);

Jest

To use opfs-mock in a single Jest test suite, require opfs-mock at the beginning of the test file, as described above.

To use it on all Jest tests without having to include it in each file, add the auto setup script to the setupFiles in your Jest config:

// jest.config.js

{
  ...
  "setupFiles": [
    "opfs-mock"
  ]
}

Alternatively you can create a new setup file which then imports this module.

// jest-setup.ts

import "opfs-mock";

Add that file to your setupFiles array:

// jest.config.js

{
  ...
  "setupFiles": [
    "jest-setup"
  ]
}

Wiping/resetting the OPFS mock for a fresh state

If you are keeping your tests completely isolated you might want to "reset" the state of the mocked OPFS. You can do this by using resetMockOPFS function, which creates a completely new instance of the mock.

import { resetMockOPFS } from 'opfs-mock';

beforeEach(() => {
  resetMockOPFS();
});

test('First isolated test', async () => {
  // rest of your test
});

test('Second isolated test', async () => {
  // rest of your test
});