function preload(images) {
    if (document.images) {
        var i = 0;
        var imageArray = new Array();
        imageArray = images.split(',');
        var imageObj = new Image();
        for (i = 0; i <= imageArray.length - 1; i++) {
            //document.write('<img src="' + imageArray[i] + '" />');// Write to page (uncomment to check images)
            imageObj.src = images[i];
        }
    }
}

function showOverlay(divId, isModal) {

    var modalOverlay = document.getElementById('modalScreen');
    var activeOverlay = document.getElementById(divId);

    if (isModal == true) {
        window.onscroll = function() {
            document.getElementById('modalScreen').style.top = document.body.scrollTop;
            document.getElementById(divId).style.top = document.body.scrollTop;
        }
        modalOverlay.style.top = document.body.scrollTop;
        modalOverlay.style.width = '100%';
        modalOverlay.style.height = '100%';
        modalOverlay.style.display = "block";

        activeOverlay.style.top = document.body.scrollTop;
        activeOverlay.style.display = "block";
    }
    else {
        window.onscroll = function() {
            document.getElementById(divId).style.top = document.body.scrollTop;
        }
        activeOverlay.style.top = document.body.scrollTop;
        activeOverlay.style.display = "block";
    }
}

function hideOverlay(divId) {
    if (document.getElementById('modalScreen').style.display == "block") {
        document.getElementById('modalScreen').style.display = "none";
    }
    document.getElementById(divId).style.display = "none";
}