function imgOn(element) {
    var image = element.src.toString();
    if (image.lastIndexOf(".") != -1)
        element.src = image.substring(0, image.lastIndexOf(".")) + "-on" + image.substring(image.lastIndexOf("."));
}

function imgOff(element) {
    var image = element.src.toString();
    if (image.lastIndexOf(".") != -1)
        element.src = image.substring(0, image.lastIndexOf(".") - 3) + image.substring(image.lastIndexOf("."));
}