Ajax

HttpRequest.prototype.createXmlHttpRequest = function ()
{
    if (window.XMLHttpRequest)
    {
        var oHttp = new XMLHttpRequest();
       
        return oHttp;
    }
    else if (window.ActiveXObject)
    {
   
        var versions =
       
        [
       
        "MSXML2.XmlHttp.6.0",
       
        "MSXML2.XmlHttp.3.0"
       
        ];
       
        for (var i = 0; i < versions.length; i++)
        {
            try
            {
                var oHttp = new ActiveXObject(versions[i]);
                return oHttp;
            }
            catch (error)
            {
                //do nothing here
            }
        }
    }
    alert("Your browser doesn’t support XMLHttp");
}

二、发送请求
// 请求服务器
function HttpRequest(sUrl, fpCallback)
{

    this.request = this.createXmlHttpRequest();//创建请求对象
   
    this.request.open("GET", sUrl, true);//请求方式，地址，是否异步请求：
   
    var tempRequest = this.request;
   
    function request_readystatechange()
    {
        if (tempRequest.readyState == 4)
        {
            if (tempRequest.status == 200)
            {
                fpCallback(tempRequest.responseText);
            }
            else
            {
                alert("An error occurred trying to contact the server.");
            }
        }
    }
   
    this.request.onreadystatechange = request_readystatechange;

}

HttpRequest.prototype.send = function ()
{
    this.request.send(null);
}