iframe communication

// FROM http://stackoverflow.com/questions/25098021/securityerror-blocked-a-frame-with-origin-from-accessing-a-cross-origin-frame

In your main page:

var frame = document.getElementById('your-frame-id');
frame.contentWindow.postMessage(/*any variable or object here*/, '*');

In your <iframe> (contained in the main page):

window.addEventListener('message', function(event) {

    // IMPORTANT: Check the origin of the data!
    if (~event.origin.indexOf('http://yoursite.com')) {
        // The data has been sent from your site

        // The data sent with postMessage is stored in event.data
        console.log(event.data);
    } else {
        // The data hasn't been sent from your site!
        // Be careful! Do not use it.
        return;
    }
});