webext-core - Browser Extension Utilities

When to Use

Apply this skill when:

package.json has any @webext-core/* dependency
Code imports defineProxyService, flattenPromise from @webext-core/proxy-service
Code imports defineExtensionMessaging, defineWindowMessaging from @webext-core/messaging
Code uses MatchPattern from @webext-core/match-patterns
Tests use fakeBrowser from @webext-core/fake-browser
Code uses defineJobScheduler from @webext-core/job-scheduler
Code uses createIsolatedElement from @webext-core/isolated-element

Quick Reference

Package	Purpose	Reference
`@webext-core/proxy-service`	Cross-context RPC — call background services from anywhere	references/proxy-service.md
`@webext-core/messaging`	Type-safe extension/window/custom event messaging	references/messaging.md
`@webext-core/match-patterns`	URL pattern matching utilities	references/match-patterns.md
`@webext-core/fake-browser`	In-memory browser API for unit testing	references/fake-browser.md
`@webext-core/job-scheduler`	Background job scheduling via Alarms API	references/job-scheduler.md
`@webext-core/isolated-element`	Shadow DOM containers for content script UIs	references/isolated-element.md
`@webext-core/storage`	localStorage-like wrapper (prefer WXT storage if using WXT)	references/storage.md
Cross-package patterns and anti-patterns	—	references/patterns.md

Most Common Pattern

// services/counter.ts
import { defineProxyService } from '@webext-core/proxy-service';

const [registerCounter, getCounter] = defineProxyService('CounterService', () => {
  let count = 0;
  return {
    increment: () => ++count,
    getCount: () => count,
  };
});

export { registerCounter, getCounter };

// background.ts — register the real implementation
registerCounter();

// popup or content script — call via proxy (all methods return Promise)
const counter = getCounter();
const newCount = await counter.increment();