// determine height of content on this page
    function getMyHeight() {
        //https://stackoverflow.com/a/11864824
        return Math.max( document.body.scrollHeight, document.documentElement.scrollHeight)
    }

    // send the latest page dimensions to the parent page on which this iframe is embedded
    function sendDimensionsToParent() {
        var iframeDimensions_New = {
                    'width': window.innerWidth, //supported from IE9 onwards
                    'height': getMyHeight()
                };
                
        // if old width is not equal new width, or old height is not equal new height, then...
        if ((iframeDimensions_New.width != iframeDimensions_Old.width) || (iframeDimensions_New.height != iframeDimensions_Old.height)) {
            window.parent.postMessage(iframeDimensions_New, "*");
            iframeDimensions_Old = iframeDimensions_New;
        }
    }


    // on load - send the page dimensions. (we do this on load because then all images have loaded...)
    window.addEventListener('load', function(){
        iframeDimensions_Old = {'width': window.innerWidth, //supported from IE9 onwards
                                'height': getMyHeight() + 5};

        window.parent.postMessage(iframeDimensions_Old, "*"); //send our dimensions once, initially - so the iFrame is initialized to the correct size

        // if mutationobserver is supported by this browser
        if (window.MutationObserver) {
            //https://developer.mozilla.org/en-US/docs/Web/API/MutationObserver

            var observer = new MutationObserver(sendDimensionsToParent);
            config = {
                  attributes: true,
                  attributeOldValue: false,
                  characterData: true,
                  characterDataOldValue: false,
                  childList: true,
                  subtree: true
            };

            observer.observe(document.body, config);
        } else {
            //check for changes on a timed interval, every 1/3 of a second
            window.setInterval(sendDimensionsToParent, 300);
        }
    });