最简单的一个ajax应用，框架什么的还没去研究呢，记录着先

	// ************ ajax
	function findAuthor(url)
	{
		var xmlObj = null;
		
		if(window.XMLHttpRequest)
		{
			xmlObj = new XMLHttpRequest();
		} 
		else if(window.ActiveXObject)
		{
			xmlObj = new ActiveXObject("Microsoft.XMLHTTP");
		} 
		else 
		{
			return;
		}
		
		xmlObj.onreadystatechange = function()
		{
			getObj('username_signal').innerHTML = "LOADING...";
			
			if(xmlObj.readyState == 4)
			{
				//var see = xmlObj.responseXML.getElementsByTagName('name')[0].firstChild.data;
				var see = xmlObj.responseText;
				
				//alert(see);
				//alert(see==1);
				if(see==1)
				{
					//when 1 , user not exist in db
					getObj('username_signal').innerHTML = "用户名可以使用！";
					username_signal = true;
				}
				else
				{
					//when 0 , user has existed in db
					getObj('username_signal').innerHTML = "用户名已经被使用，换一个吧！";
					username_signal = false;
				}
			}
		}
		xmlObj.open ('GET', url, true);
		xmlObj.send ('');
		
	}