//globals 
var first = "state"; //id of first select 
var second = "city"; //id of second select 
// 
function sendRequest(url,HttpMethod) { 
	if(!HttpMethod) { //check if http method is defined, if not, set it to GET    
		HttpMethod="GET"; 
	} 
// 
// initialize request object 
	req=null; 
	if(window.XMLHttpRequest){    
		req=new XMLHttpRequest; //mozilla/safari 
	} else if(window.ActiveXObject){    
		req=new ActiveXObject("Microsoft.XMLHTTP"); //internet explorer 
	} 
// 
//define callback handler 
	if(req) { 
	//  
		req.onreadystatechange=onReadystate;    
		req.open(HttpMethod,url,true);    
		req.setRequestHeader("Content-Type","application/x-www-form-urlencoded");    
		req.send(null);
	} 
} 
// 
function onReadystate() { 
// 
	var ready=req.readyState; 
	var data=null;
	if(ready==4){ //check ready state    
		data=req.responseText; //read response data
		var items = data.split(',');    
		var length = items.length;
			for(var i = 0; i < length; i++) {
				var childEl = document.createElement('option'); //create option
				var El = document.getElementById(second);
				El.appendChild(childEl); //then append it to the second dropdown list       
				childEl.value = items[i];       
				childEl.innerHTML = items[i];
			} 
	} 
} 
// 
function clicked() { 
// 
var el = document.getElementById(first); 
var ob2=document.getElementById(second); 
var selected = el.selectedIndex;
// 
while(ob2.hasChildNodes()) { //removes items from dropdown if some already exist    
	ob2.removeChild(ob2.firstChild); 
} 
if(selected!= 0) { //if they choose something other than the first select-->"select topic first"
	sendRequest('get_city.php?topic='+el.options[selected].value);    
	ob2.disabled=0; 
} else { //otherwise add the select Topic First option and disable it    
	var childEl = document.createElement('option');    
	ob2.appendChild(childEl);    
	childEl.innerHTML = 'select Topic First';    
	ob2.disabled=1; 
} 
} 

window.onload = init;
window.onunload = GUnload;