90Implement synchronization between browser tabs using BroadcastChannel

A user opens your app in three tabs, changes the theme in one and logs out in another. Every tab should reflect both changes without a reload.

Implement createSyncedStore(channelName, initialState) on top of BroadcastChannel:

• getState() and subscribe(listener) (returns an unsubscribe function); listeners receive the new state.
• setState(partial) merges partial into the state, notifies local listeners, and broadcasts the change to the other tabs.
• When a message arrives from another tab, apply it and notify local listeners, without broadcasting it again (no echo loops).
• A tab that opens later asks the existing tabs for the current state and adopts the newest answer.
• Concurrent updates must converge: give every change a version (a counter that is always bumped above the highest version seen, a Lamport clock) plus the tab id as a tie-breaker, and apply a remote change only if it is newer than what the tab already has.
• close() closes the channel.

const session = createSyncedStore("session", { theme: "light", user: { name: "Asha" } });
session.subscribe((state) => applyTheme(state.theme));
logoutButton.onclick = () => session.setState({ user: null }); // every tab logs out