Broadcast Channel Mocking with Vitest

This JavaScript module provides a way to mock the BroadcastChannel API for testing purposes using Vitest, a fast and type-safe testing framework.

Install

Before using this module, ensure that you have Vitest installed in your project. If not, you can install it via npm:

npm install vitest --save-dev

You can then import the mock functions in your tests:

import { mockBroadcastChannel, resetMockBroadcastChannel } from 'vitest-mock-broadcast-channel';

Usage

This module exports two main functions:

1. mockBroadcastChannel(): Sets up a mock version of the BroadcastChannel global and returns a map of mock channel objects.

2. resetMockBroadcastChannel(): Clears all mock channels and restores the original global functions, useful for cleanup after each test.

A mock channel object replicates the functionality of a real BroadcastChannel object, with methods like postMessage(), addEventListener(), etc. These methods are all mocked using Vitest's vi.fn() function.

Example:

import { mockBroadcastChannel, resetMockBroadcastChannel } from './path/to/mockBroadcastChannel';

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

afterEach(() => {
  resetMockBroadcastChannel();
});

it('tests BroadcastChannel', () => {
  const channel = new BroadcastChannel('myChannel');

  // Now you can test your code that relies on BroadcastChannel API
  // All the channel methods are now mocked and can be controlled for testing purposes
});

Notes

The postMessage method on a mock channel works slightly differently than the real one. Instead of sending a message to all other instances of the same channel, it will invoke any function that has been passed to addEventListener with an event object that has the posted message as its data property.

This module doesn't replicate the asynchronous nature of the real postMessage. It calls the event listener functions synchronously.

License

This project is open sourced under the MIT License.

Contribution

Contributions are welcome! Please open an issue if you find a bug or have a feature request. You can also propose changes via a pull request.

Author

Eddy Brown - GitHub