Failed to execute 'postMessage' on 'DOMWindow':

Question

When I create a SharePoint Provider hosted App in visual studio, visual studio creates two projects: App and web application. both projects runs over HTTPS
I created a list in the App and entered some random data. Now, I need to get the data I entered from the web application using CSOM. When I try to get it through cross domain library (SP.RequestExecuter.Js) but I get the following error:
Here is my code:
function execCSOMListRequest() {
    var context;
    var factory;
    var appContextSite;
    var collList;
    //Get the client context of the AppWebUrl
    context = new SP.ClientContext(appwebUrl);
    //Get the ProxyWebRequestExecutorFactory
    factory = new SP.ProxyWebRequestExecutorFactory(appwebUrl);
    //Assign the factory to the client context.
    context.set_webRequestExecutorFactory(factory);
    //Get the app context of the Host Web using the client context of the Application.
    appContextSite = new SP.AppContextSite(context, hostwebUrl);
    //Get the Web
    this.web = context.get_web();
    // Get the Web lists.
    collList = this.web.get_lists();
    //Load Lists.
    context.load(collList);
    context.executeQueryAsync(
        Function.createDelegate(this, successListHandlerCSOM),
        Function.createDelegate(this, errorListHandlerCSOM)
    //Success Lists
    function successListHandlerCSOM() {
        var listEnumerator = collList.getEnumerator();
        $('#lblResultLists').html("<b>Via CSOM the lists are:</b><br/>");
        while (listEnumerator.moveNext()) {
            var oList = listEnumerator.get_current();
            $('#lblResultLists').append(oList.get_title() + " (" + oList.get_itemCount() + ")<br/>");
    //Error Lists
    function errorListHandlerCSOM(data, errorCode, errorMessage) {
        $('#lblResultLists').html("Could not complete CSOM Call: " + errorMessage);
Any solution ?

Answer 1

Part of Standard Mashup js Code that gets invoked when you click on Preview:
// HTML5: window.postMessage
        if (isHostMethod(window, 'postMessage') || isHostMethod(document, 'postMessage')) {
            protocol = '0';
        // IE8-
        else {
            alert('This product only supports IE8(+) & Firefox.');
        if (protocol == '0') {
            //host
            if (isHost) {
                remoteDomain = config.remoteDomain;
                remote = targetDoc.getElementById(config.frameId).contentWindow;
                on(window, 'message', hostOnMsg);
                timer = setInterval(syn, 500);
            //guest
            else {
                this.closeWindow = function () {
                    this.postMessage('CLOSE');
                on(window, 'message', guestOnMsg);
            this.postMessage = function (message) {
               remote.postMessage(message, remoteDomain);
Line marked with red is the one stopping you from viewing mashups. I believe you are not using InternetExplorer because as per what I see in this code, the red line doesn't get executed when you try to preview using IE.
Even, I am able to replicate your problem in Chrome but not in IE. Did you try in IE already(preferably >= 8)?