// JavaScript Document
//初始化AJAX
var xmlHttp;
function createXMLHttpRequest(){
	//如果是IE，用activexobject
	if (window.ActiveXObject) {
		xmlHttp = new ActiveXObject("Microsoft.XMLHTTP");
	}else if (window.XMLHttpRequest) {
		xmlHttp = new XMLHttpRequest();
	}else{
		window.alert("不能创建XMLHttpRequest对象实例.");
	}
}

//用GET发送请求
function sendGetXMLHttpRequest(geturl,callback, parameter, obj){
	createXMLHttpRequest();
	xmlHttp.onreadystatechange = function (){handleStateChange(callback,parameter,obj)};
	xmlHttp.open("GET",geturl,false);
	xmlHttp.send(null);
}

//用POST发送请求
function sendPostXMLHttpRequest(posturl,callback,parameter){
	createXMLHttpRequest();
	xmlHttp.onreadystatechange = function (){handleStateChange(callback)};
	xmlHttp.open("POST",posturl,false);
	xmlHttp.setRequestHeader("Content-Type", "application/x-www-form-urlencoded"); 
	parameter = encodeURI(parameter);
	parameter = encodeURI(parameter);
	xmlHttp.send(parameter);
}

//获得请求
function handleStateChange(callback,parameter,obj){
	if(xmlHttp.readyState == 4) {
		//200返回请求状态为OK
		if(xmlHttp.status == 200) {
			var fn = callXmlHttpRequest(callback, parameter,obj);
			fn();
		}else{
			alert(xmlHttp.statusText);
		}
	}
}

//反向调用方法
function callXmlHttpRequest(callback,parameter, obj){
	return function(){	//这里返回一个有参数的Function
		callback(parameter, obj);//调用参数传入的函数
	}
}