MessageChannel

Entangled ports

A message channel is two MessagePorts born already connected. A message posted on one is delivered only at the other.

	You hold	Who hears	AuthZ
MessageChannel	A port	The entangled twin	Who you gave the port to
window.postMessage	A window	That window’s listeners	`targetOrigin` + `event.origin`
BroadcastChannel	A name	Every same-origin subscriber	Same origin + same name
Same-context call	A function	Whoever you invoked	Ordinary JS visibility

const { port1, port2 } = new MessageChannel();
port1.onmessage = (e) => console.log(e.data);
port2.postMessage("hello");