给初学ajax的人 ajax函数代码

代码如下:
/*
调用方式:
1.POST方式
var txt = escape(sender.value); //document.getElementById("<%= txtName.ClientID %>").value);
var data = "name=" + txt + "&pwd=" + txt;
var option = { "url": "handler/Handler.ashx"
, "action": "POST"
, "callback": function(){
if (xmlHttp.readyState == 4) {//服务器给了回应
if (xmlHttp.status == 200) {//服务正确响应
alert(xmlHttp.responseText);
}
xmlHttp = null; //回收资源
}
　　　}
, "data": data
};
ajax(option);
2.GET方式
var txt = escape(sender.value); //document.getElementById("<%= txtName.ClientID %>").value);
var option = { "url": "handler/Handler.ashx&name=" + txt + "&pwd=" + txt
, "action": "POST"
, "callback": function(){
if (xmlHttp.readyState == 4) {//服务器给了回应
if (xmlHttp.status == 200) {//服务正确响应
alert(xmlHttp.responseText);
}
xmlHttp = null; //回收资源
}
　　　}
};
ajax(option);
*/
function ajax(option) {
createXMlHttpRequest(); //创建xmlHttpRequest 对象
if (option != null && option != undefined) {
if (option.url == null && option.url == undefined) {
xmlHttp = null;
alert("缺少必要参数option.url");
return;
}
if (option.action == null && option.action == undefined) {
xmlHttp = null;
alert("缺少必要参数option.action");
return;
}
xmlHttp.open(option.action, option.url, true);
if (option.contentType != null && option.contentType != undefined) {
xmlHttp.setRequestHeader("Content-Type", option.contentType);
} else {
xmlHttp.setRequestHeader("Content-Type", "application/x-www-form-urlencoded");
}
if (option.callback != null && option.callback != undefined) {
xmlHttp.onreadystatechange = option.callback;
}
if (option.action.toUpperCase() == "POST") {
xmlHttp.send(option.data);
} else {
xmlHttp.send(null);
}
}
}
var xmlHttp; //调用完成后最好回收下 xmlHttp = null;
/*获取元素*/
function g(arg) {
var t = document.getElementById(arg);
if (null != t && t != undefined) {
return t;
}
t = document.getElementsByName(arg);
if (null != t && t != undefined) {
return t;
}
t = document.getElementsByTagName(arg);
if (null != t && t != undefined) {
return t;
}
}
/*创建ajax请求对象*/
function createXMlHttpRequest() {
try {//Firefox, Chrome, Surfri, Opera+8
xmlHttp = new XMLHttpRequest();
}
catch (ie) {
try {//IE6+
xmlHttp = new ActiveXObject("Msxml2.XMLHTTP");
} catch (ie) {
xmlHttp = new ActiveXObject("Microsoft.XMLHTTP");
}
}
return xmlHttp;
}