function changeBack(obj,color)
{
    obj.style.background = color;
}
// ajax functions
var xmlHttp
<!----------NTContent------------------------------------------------------------------->
var target
	
function showContent(file,targetF)
{ 

	target = targetF;
	var url=""+file+"";
	xmlHttp=GetXmlHttpObject(stateChanged)
	xmlHttp.open("GET", url , true)
	xmlHttp.send(null)
} 

function stateChanged() 
{ 
if (xmlHttp.readyState==1 || xmlHttp.readyState==2)
{ 
	document.getElementById(target).innerHTML='<img src="./images/loading.gif">';

} 

  else  if (xmlHttp.readyState==4 || xmlHttp.readyState=="200")
{ 
	document.getElementById(target).innerHTML=xmlHttp.responseText 
	window.status="Đã tải xong dữ liệu !";

}  
}
<!----------NTContent------------------------------------------------------------------->

<!------------------------Show hide--------------------------------------------------------->
function crossObj(id){
 if (document.getElementById) {
  	return document.getElementById(id);
 } else if (document.all) {
  	return document.all[id];
 } else if (document.layers) {
  	return document.layers[id];
 } else {
  	return null;
 }
}

function getO(id) {
 	return crossObj(id);
}

function hideO(id) {
 	getO(id).style.display = 'none';
}

function showO(id) {
 	getO(id).style.display = '';
}

<!------------------------Show hide--------------------------------------------------------->

function GetXmlHttpObject(handler)
{ 
	var objXmlHttp=null

	if (navigator.userAgent.indexOf("Opera")>=0)
	{
		alert("This example doesn't work in Opera") 
		return 
	}
	if (navigator.userAgent.indexOf("MSIE")>=0)
	{ 
		var strName="Msxml2.XMLHTTP"
		if (navigator.appVersion.indexOf("MSIE 5.5")>=0)
	{
		strName="Microsoft.XMLHTTP"
	} 
	try
	{ 
		objXmlHttp=new ActiveXObject(strName)
		objXmlHttp.onreadystatechange=handler 
		return objXmlHttp
	} 
	catch(e)
	{ 
		alert("Error. Scripting for ActiveX might be disabled") 
		return 
	} 
	} 
	if (navigator.userAgent.indexOf("Mozilla")>=0)
	{
		objXmlHttp=new XMLHttpRequest()
		objXmlHttp.onload=handler
		objXmlHttp.onerror=handler 
		return objXmlHttp
	}
}