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.

Specification

partial interface Window {
    MessagePort connectTo(DOMString target);
};

The connectTo method opens a message port to a browsing context with name target within the caller's origin (although not necessarily within the caller's unit of related browsing contexts).

1. Create a new MessagePort object owned by the global object of the incumbent script. Let this be the outside port.
2. Return the outside port and continue executing the following steps asynchronously.

Examples

Listener

window.addEventListener("connect", function(message) {
  // 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("Welcome!");
  // 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 port = window.connectTo("the-listener");

port.addEventListener("message", function(message) {
  if (message.data == "Welcome!")
    alert("Success!);
}, false);

port.start();