For: https://twitter.com/JoelStransky/status/1774913968588698107

content-cache.js

import { useSyncExternalStore } from 'react'

/**
 * This will call the given callback function whenever the contents of the map
 * change.
 */
class ObservableMap extends Map {
	constructor(entries) {
		super(entries)
		this.listeners = new Set()
	}
	set(key, value) {
		const result = super.set(key, value)
		this.emitChange()
		return result
	}
	delete(key) {
		const result = super.delete(key)
		this.emitChange()
		return result
	}
	emitChange() {
		for (const listener of this.listeners) {
			listener()
		}
	}
	subscribe(listener) {
		this.listeners.add(listener)
		return () => {
			this.listeners.delete(listener)
		}
	}
}
export const contentCache = new ObservableMap()

export function useContentCache() {
	function subscribe(cb) {
		return contentCache.subscribe(cb)
	}
	function getSnapshot() {
		return contentCache
	}
	return useSyncExternalStore(subscribe, getSnapshot)
}