var lastDiv = "";
function showDiv(divName) {
	// hide last div
	if (lastDiv) {
		document.getElementById(lastDiv).className = "hiddenDiv";
	}
	//if value of the box is not nothing and an object with that name exists, then change the class
	if (divName && document.getElementById(divName)) {
		document.getElementById(divName).className = "visibleDiv";
		lastDiv = divName;
	}
}