bext

Tools for Building Browser Extensions with Deno. Supports Chromium and Firefox browsers.

Usage

You can see examples/preact as an example of basic usage and how to setup a working environment.

You can also see a real-world example by looking at Favioli.

Bundle

Once you have an app structured, bext can bundle your extension for Chrome and Firefox using esbuild. It will also take browser-specific properties from your manifest.json file, and format them into a compatible structure for each browser.

> deno install -gA --name=bext jsr:@bpev/bext/bin

> cd ./my_project

> bext # both
> bext chrome # only chrome
> bext firefox # only ff

> bext --watch # build again on change
> bext chrome -w # variations can be used for single-platform
> bext firefox --watch

Types and Utilities

While building your app, bext re-exports the native extension apis, to smooth out a few of the cross-platform differences. We also add a couple utility functions to determine which browser we are using.

// Import the direct npm:@types/chrome import used to define browserAPI in Bext
// Alternatively, `import { Tab, TabChangeInfo } from npm:@types/chrome`
import type Chrome from 'jsr:@bpev/bext/types/chrome'

/**
 * browserAPI resolves to:
 *   - globalThis.chrome in Chromium browsers
 *   - globalThis.browser in Firefox browsers
 *   - Bext's mock_browser in Deno context (for unit testing)
 */
import browserAPI, { isChrome, isFirefox } from 'jsr:@bpev/bext'

browserAPI.tabs.onUpdated.addListener(
  (tabId: number, _: Chrome.TabChangeInfo, tab: Chrome.Tab) => {
    console.log(isChrome(), isFirefox())
  },
)

Testing

bext browserAPI will also return a mock browser when running in a Deno environment (where native extension apis don't exist). This makes writing unit tests a breeze!

import browserAPI, { isDeno } from 'jsr:@bpev/bext';
import { assertStrictEquals } from 'jsr:@std/assert';
import { assertSpyCall, assertSpyCalls, stub } from 'jsr:@std/testing/mock';

import { getStorage } from './storage_helpers.ts';

Deno.test('is running in test env', () => {
  assert()
})

Deno.test('uses browser storage', async () => {
  const getStorageStub = stub(browserAPI.storage.sync, 'get', () => {
    return Promise.resolve({ storage_key: 'mock_storage_value' });
  });

  assertStrictEquals(await getStorage(), 'mock_storage_value');
  assertSpyCalls(getStorageStub, 1);

  // Expect `chrome.sync.storage.get` to be called with the storage_key
  assertSpyCall(getStorageStub, 0, { args: ['storage_key'] });
  getStorageStub.restore();
});

Running this repo (for Bext development)

Tasks are defined in deno.json, but basically:

• deno task dev: Run the example app in watch-mode
• deno task test: Makes sure it all works. Use this before committing!
  • runs fmt, lint, type-checks, unit tests for source and example apps
  • builds example apps using local bext copy