Comctx NPM | npm.io

Comctx

Cross-context RPC solution with type safety and flexible adapters.

$ pnpm install comctx

✨Introduction

Comctx shares the same goal as Comlink, but it is not reinventing the wheel. Since Comlink relies on MessagePort, which is not supported in all environments, this project implements a more flexible RPC approach that can more easily and effectively adapt to different runtime environments.

💡Features

Environment Agnostic - Works across Web Workers, Browser Extensions, iframes, Electron, and more
Bidirectional Communication - Method calls & callback support
Type Safety - Full TypeScript integration
Lightweight - 1KB gzipped core
Fault Tolerance - Backup implementations & connection health checks

🚀 Quick Start

Define a Shared Service

import { defineProxy } from 'comctx'

class Counter {
  public value = 0
  async getValue() {
    return this.value
  }
  async onChange(callback: (value: number) => void) {
    let oldValue = this.value
    setInterval(() => {
      const newValue = this.value
      if (oldValue !== newValue) {
        callback(newValue)
        oldValue = newValue
      }
    })
  }
  async increment() {
    return ++this.value
  }
  async decrement() {
    return --this.value
  }
}

export const [provideCounter, injectCounter] = defineProxy(() => new Counter(), {
  namespace: '__comctx-example__'
})

Provider (Service Provider)

// provide end, typically for service-workers, background, etc.
import type { Adapter, SendMessage, OnMessage } from 'comctx'
import { provideCounter } from './shared'

export default class ProvideAdapter implements Adapter {
  // Implement message sending
  sendMessage: SendMessage = (message) => {
    postMessage(message)
  }
  // Implement message listener
  onMessage: OnMessage = (callback) => {
    const handler = (event: MessageEvent) => callback(event.data)
    addEventListener('message', handler)
    return () => removeEventListener('message', handler)
  }
}

const originCounter = provideCounter(new ProvideAdapter())

originCounter.onChange(console.log)

Consumer (Service Consumer)

// inject end, typically for the main page, content-script, etc.
import type { Adapter, SendMessage, OnMessage } from 'comctx'
import { injectCounter } from './shared'

export default class InjectAdapter implements Adapter {
  // Implement message sending
  sendMessage: SendMessage = (message) => {
    postMessage(message)
  }
  // Implement message listener
  onMessage: OnMessage = (callback) => {
    const handler = (event: MessageEvent) => callback(event.data)
    addEventListener('message', handler)
    return () => removeEventListener('message', handler)
  }
}

const proxyCounter = injectCounter(new InjectAdapter())

// Support for callbacks
proxyCounter.onChange(console.log)

// Transparently call remote methods
await proxyCounter.increment()
const count = await proxyCounter.getValue()

originCounter and proxyCounter will share the same Counter. proxyCounter is a virtual proxy, and accessing proxyCounter will forward requests to the Counter on the provide side, whereas originCounter directly refers to the Counter itself.
The inject side cannot directly use get and set; it must interact with Counter via asynchronous methods, but it supports callbacks.
Since inject is a virtual proxy, to support operations like Reflect.has(proxyCounter, 'value'), you can set backup to true, which will create a static copy on the inject side that doesn't actually run but serves as a template.
provideCounter and injectCounter require user-defined adapters for different environments that implement onMessage and sendMessage methods.

🔌 Adapter Interface

To adapt to different communication channels, implement the following interface:

interface Adapter<M extends Message = Message> {
  /** Send a message to the other side */
  sendMessage: (message: M) => MaybePromise<void>

  /** Register a message listener */
  onMessage: (callback: (message?: Partial<M>) => void) => MaybePromise<OffMessage>
}

📖Examples

Service Worker

This is an example of communication between the main page and an service-worker.

see: service-worker-example

InjectAdpter.ts

import { Workbox, WorkboxMessageEvent } from 'workbox-window'
import { Adapter, SendMessage, OnMessage } from 'comctx'

export default class InjectAdapter implements Adapter {
  workbox: Workbox
  constructor(path: string) {
    this.workbox = new Workbox(path, { type: import.meta.env.MODE === 'production' ? 'classic' : 'module' })
    this.workbox.register()
  }
  sendMessage: SendMessage = (message) => {
    this.workbox.messageSW(message)
  }
  onMessage: OnMessage = (callback) => {
    const handler = (event: WorkboxMessageEvent) => callback(event.data)
    this.workbox.addEventListener('message', handler)
    return () => this.workbox.removeEventListener('message', handler)
  }
}

ProvideAdpter.ts

import { Adapter, SendMessage, OnMessage } from 'comctx'

declare const self: ServiceWorkerGlobalScope

export default class ProvideAdapter implements Adapter {
  sendMessage: SendMessage = (message) => {
    self.clients.matchAll().then((clients) => {
      clients.forEach((client) => client.postMessage(message))
    })
  }
  onMessage: OnMessage = (callback) => {
    const handler = (event: ExtendableMessageEvent) => callback(event.data)
    self.addEventListener('message', handler)
    return () => self.removeEventListener('message', handler)
  }
}

servie-worker.ts

import { provideCounter } from './shared'
import ProvideAdapter from './ProvideAdapter'

declare const self: ServiceWorkerGlobalScope

self.addEventListener('install', () => {
  console.log('ServiceWorker installed')
  self.skipWaiting()
})
self.addEventListener('activate', (event) => {
  console.log('ServiceWorker activated')
  event.waitUntil(self.clients.claim())
})

const counter = provideCounter(new ProvideAdapter())

counter.onChange((value) => {
  console.log('ServiceWorker Value:', value) // 1,0
})

main.ts

import { injectCounter } from './shared'
import InjectAdapter from './InjectAdapter'

const counter = injectCounter(
  new InjectAdapter(import.meta.env.MODE === 'production' ? '/service-worker.js' : '/dev-sw.js?dev-sw')
)

counter.onChange((value) => {
  console.log('ServiceWorker Value:', value) // 1,0
})

await counter.getValue() // 0

await counter.increment() // 1

await counter.decrement() // 0

Browser Extension

This is an example of communication between the content-script page and an background.

see: browser-extension-example

InjectAdpter.ts

import browser from 'webextension-polyfill'
import { Adapter, Message, SendMessage, OnMessage } from 'comctx'

export interface MessageExtra extends Message {
  url: string
}

export default class InjectAdapter implements Adapter<MessageExtra> {
  sendMessage: SendMessage<MessageExtra> = (message) => {
    browser.runtime.sendMessage(browser.runtime.id, { ...message, url: document.location.href })
  }
  onMessage: OnMessage<MessageExtra> = (callback) => {
    const handler = (message: any): undefined => {
      callback(message)
    }
    browser.runtime.onMessage.addListener(handler)
    return () => browser.runtime.onMessage.removeListener(handler)
  }
}

ProvideAdapter.ts

import browser from 'webextension-polyfill'
import { Adapter, Message, SendMessage, OnMessage } from 'comctx'

export interface MessageExtra extends Message {
  url: string
}

export default class ProvideAdapter implements Adapter<MessageExtra> {
  sendMessage: SendMessage<MessageExtra> = async (message) => {
    const tabs = await browser.tabs.query({ url: message.url })
    tabs.map((tab) => browser.tabs.sendMessage(tab.id!, message))
  }

  onMessage: OnMessage<MessageExtra> = (callback) => {
    const handler = (message: any): undefined => {
      callback(message)
    }
    browser.runtime.onMessage.addListener(handler)
    return () => browser.runtime.onMessage.removeListener(handler)
  }
}

background.ts

import { provideCounter } from './shared'
import ProvideAdapter from './ProvideAdapter'

const counter = provideCounter(new ProvideAdapter())

counter.onChange((value) => {
  console.log('Background Value:', value) // 1,0
})

content-script.ts

import { injectCounter } from './shared'
import InjectAdapter from './InjectAdapter'

const counter = injectCounter(new InjectAdapter())

counter.onChange((value) => {
  console.log('Background Value:', value) // 1,0
})

await counter.getValue() // 0

await counter.increment() // 1

await counter.decrement() // 0

IFrame

This is an example of communication between the main page and an iframe.

see: iframe-example

InjectAdapter.ts

import { Adapter, SendMessage, OnMessage } from 'comctx'

export default class InjectAdapter implements Adapter {
  sendMessage: SendMessage = (message) => {
    window.postMessage(message, '*')
  }
  onMessage: OnMessage = (callback) => {
    const handler = (event: MessageEvent) => callback(event.data)
    window.addEventListener('message', handler)
    return () => window.removeEventListener('message', handler)
  }
}

ProvideAdapter.ts

import { Adapter, SendMessage, OnMessage } from 'comctx'

export default class ProvideAdapter implements Adapter {
  sendMessage: SendMessage = (message) => {
    window.parent.postMessage(message, '*')
  }
  onMessage: OnMessage = (callback) => {
    const handler = (event: MessageEvent) => callback(event.data)
    window.parent.addEventListener('message', handler)
    return () => window.parent.removeEventListener('message', handler)
  }
}

iframe.ts

import { provideCounter } from './shared'
import ProvideAdapter from './ProvideAdapter'

const counter = provideCounter(new ProvideAdapter())

counter.onChange((value) => {
  console.log('iframe Value:', value) // 1,0
})

main.ts

import { injectCounter } from './shared'
import InjectAdapter from './InjectAdapter'

const counter = injectCounter(new InjectAdapter())

counter.onChange((value) => {
  console.log('iframe Value:', value) // 1,0
})

await counter.getValue() // 0

await counter.increment() // 1

await counter.decrement() // 0