ump-plugin-broadcast-channel

Single-realm WHATWG BroadcastChannel polyfill for UMP apps.

Install

npm install ump-plugin-broadcast-channel

Peer dependencies (must already be installed in your app):

• ump-core
• ump-native

Usage

import { BroadcastChannel } from 'ump-plugin-broadcast-channel';

const a = new BroadcastChannel('room-1');
const b = new BroadcastChannel('room-1');

b.onmessage = (ev) => {
    console.log('got:', ev.data);
};

a.postMessage({ hello: 'world' });

// cleanup
a.close();
b.close();

Importing the module also installs globalThis.BroadcastChannel (only when the host has not already provided one), so libraries that reach for the bare global name (idb-keyval, tab-sync helpers, etc.) work without explicit import.

Scope

This is the same-realm shim used inside ump-native. Two channels with the same name running in the same JS realm exchange messages; cross-tab, cross-iframe, or cross-process delivery is not implemented because native UMP runs in a single JSEngine. Each Worker is its own realm with its own registry — use the worker handle's postMessage / onmessage for thread-to-thread comms.

On H5, the browser's built-in BroadcastChannel wins (full cross-tab semantics).

Migration from ump-native

In ump-native 0.1.x, BroadcastChannel was bundled with the main package as a side-effect global. Starting 0.2.x, it ships as this separate plugin.

- import 'ump-native'; // side-effect: globalThis.BroadcastChannel installed
+ import { BroadcastChannel } from 'ump-plugin-broadcast-channel';

No API changes. Importing the plugin still installs the global as a side-effect (non-overwriting), so existing call-sites that use the bare global name continue to work.