window.postMessage to script.google.com as popup

Question

When run: MyPopWindow.postMessage("Test", 'mydomaine'); I have a error on MyPopWindow whith script.google.com:

(program):1 Failed to execute 'postMessage' on 'DOMWindow': The target origin provided ('mydomaine') does not match the recipient window's origin ('https://script.google.com').

When run: MyPopWindow.postMessage("Test", 'https://script.google.com'); I have a error on MyPopWindow:

dropping postMessage.. was from host mydomaine but expected host https : // ******-script.googleusercontent.com

Source in page on mydomaine:

  window.addEventListener("DOMContentLoaded", function() {
    window.addEventListener("message", function(e) {
        // wait for child to signal that it's loaded.
        if ( e.data === "loaded" && e.origin === iframe.src.split("/").splice(0, 3).join("/")) {
            // send the child a message.
            alert(e.data);
        }
    })
}, false)

Source on my Google Apps Script runing as WebApp:

        document.addEventListener('DOMContentLoaded', function () {
            // signal the parent that we're loaded.
            window.parent.postMessage("loaded", "*");
            
            // listen for messages from the parent.
            window.addEventListener("message", function(e) {
            if(event.origin !== 'mydomain') return;
                  var message = e.data;
                  alert(message);
            }, false);
        });

Answer 1

This error message comes from one of App Scripts Javascript driver files. This is extra security Google added on to prevent people from using the postMessage system.

It seems Google wants to force you to use one of their accepted protocols for communication between windows/domains, namely the Execution API. I have attempted other methods like passing URL parameters, but so far none have worked because I could not access them from within the iframe that all apps scripts run in.

I believe the Execution API is your best bet.