MessageChannel API

A MessageChannel API.

Installation

Install this package as a dependency in the project:

# npm
npm i message-channel-api

# Yarn
yarn add message-channel-api

# pnpm
pnpm add message-channel-api

# Bun
bun add message-channel-api

Usage

For using the API directly:

import { MessageChannel } from "message-channel-api";

const channel: MessageChannel = new MessageChannel();

channel.port2.onmessage = (event: MessageEvent<unknown>): void => {
    console.log(event.data);
};

channel.port1.postMessage("hello");

For importing the polyfill, add the following to the entry:

import "message-channel-api/polyfill";

Compatibility

The following is a summary of the compatibility for this package.

Runtime Compatibility

• Build target: ES2015
• Package format: TypeScript declarations, ESModule, CommonJS
• Install target selection: self > window > globalThis > global
• Required ES2015 built-ins: Promise, WeakMap, Map, Set
• Supported missing globals: Event, EventTarget, MessageEvent, queueMicrotask, structuredClone

MessageChannel API Compatibility

The compatibility list below follows the API surface listed by MDN in MessageChannel.

API surface	Support	Notes
MessageChannel	Supported	Exported as MessageChannelPolyfill and aliased as MessageChannel.
port1	Supported	Exposes one side of the entangled port pair.
port2	Supported	Exposes the other side of the entangled port pair.

MessagePort API Compatibility

The compatibility list below follows the API surface listed by MDN in MessagePort.

API surface	Support	Notes
MessagePort	Supported	Supports postMessage(), start(), close(), onclose, onmessage, onmessageerror, addEventListener(), and removeEventListener() for port events.
start()	Supported	Queued messages flush after start(). Assigning onmessage also starts the receiving port.
postMessage()	Partial	Messages are cloned and delivered asynchronously. Transfer lists are forwarded only when native structuredClone() supports them, and native-style MessagePort transfer plus MessageEvent.ports population are not implemented.
close()	Supported	Closing one port detangles both ports and dispatches close on the peer port.
message event	Supported	Works with both addEventListener("message", ...) and onmessage.
messageerror event	Partial	onmessageerror exists, but messageerror events are not currently dispatched. Clone failures throw DataCloneError from postMessage().

Additional notes:

• Without native structuredClone(), cloning is limited to common built-in data types such as primitives, plain objects, arrays, Map, Set, Date, RegExp, ArrayBuffer, SharedArrayBuffer, DataView, and typed arrays.
• The event behavior is implemented for MessagePort usage, not as a full DOM EventTarget replacement.

License

This project is licensed under the terms of the MIT license.