封装异步请求操作

服务器端请求文件

//JSON_server.js
[{
	name:"css8",
	pass:"123456"
},
{
	name:"w3c",
	pass:"111111"
}]
					    

JS

// 封装创建XMLHttpRequest对象
function createXMLHTTPObject()
{
    var XMLHttpFactories = [
		function () {return new XMLHttpRequest()},
		function () {return new ActiveXObject("Msxml2.XMLHTTP")},
		function () {return new ActiveXObject("Msxml3.XMLHTTP")},
		function () {return new ActiveXObject("Microsoft.XMLHTTP")}
	];
    var xmlhttp = false;
    for (var i = 0; i < XMLHttpFactories.length; i ++ )
    {
        try
        {
            xmlhttp = XMLHttpFactories[i]();
        }
        catch (e)
        {
            continue;
        }
        break;
    }
    return xmlhttp;
}
//封装异步请求函数
function request(url, callback, data)
{
    var xmlHttp = createXMLHTTPObject();
    if ( ! xmlHttp) return;
    var method = (data) ? "POST" : "GET";
    xmlHttp.open(method, url, true);
    xmlHttp.setRequestHeader('User-Agent', 'XMLHTTP/1.0');
    if (data)
    xmlHttp.setRequestHeader('Content-type', 'application/x-www-form-urlencoded');
    xmlHttp.onreadystatechange = function ()
    {
        if (xmlHttp.readyState != 4) return;
        if (xmlHttp.status != 200 && xmlHttp.status != 304)
        {
            alert('HTTP请求错误  ' + xmlHttp.status);
            return;
        }
        callback(xmlHttp);
    }
    if (xmlHttp.readyState == 4) return;
    xmlHttp.send(data);
}
//定义请求地址
var url = "JSON_server.js";
//定义回调函数，参数为XMLHttpRequest对象
var callback = function(xmlHttp){
        var info = xmlHttp.responseText;
        var  o = eval("(" + info + ")");
        alert(info);
        alert(o[1].name);	
	
}
//调用请求函数
request(url, callback);