RemoteDocumentMessaging

Overview

This document describes a proposal for discovering and communicating with "remote" documents. In particular, this proposal lets a web page communicate with another document even if the web page does not have a direct script connection to that document.

Use Cases

The user opens the same word processing document hosted by a document editing web site in two different browser windows. The document editing web site wants to ensure that edits in one window a reflected in the other window without needing to round-trip through the server (e.g., because the user is offline). Unfortunately, the documents are in different units of related browsing contexts, which means the two documents cannot form a direct script connection. Using remote document messaging, the two documents can discover each other and update each other about edits performed by the user.

Examples

Listener

window.addEventListener("message", function(message) {
  if (message.origin != location.origin)
    return;
  if (message.data != "Hi there!")
    return;
  // message.source is a MessagePort we can use to talk to the remote message, just like in a shared worker.
  var remote = message.source;
  remote.postMessage("Thanks for the message!");
  // You can call remote.addEventListener("message", ... ) to continue communicating with the remote window.
}, false);

// Naming your window makes you discoverable by other documents in your origin.
window.name = "the-listener";

Sender

var remote = window.connectTo("the-listener");
if (!remote)
  return; // Couldn't find a remote window with the proper name in this origin.
remote.addEventListener("message", function(message) {
  if (message.data == "Thanks for the message!")
    alert("Success!);
}, false);

remote.postMessage("Hi there!");