ajax异步调用过程

JS代码：

function example()
{
   var req = getReq();
   req.open("GET", "QuerybyActionSample.aspx?name=" + escape(Name), true);
   req.onreadystatechange = function() {
   if (req.readyState == 4) {
             str = req.responseText;
             showMessage(str);
        }
    };
    req.send(null);
}
               
function getReq() {
    var oHttpReq = null;
    if (window.ActiveXObject)
         {oHttpReq = new ActiveXObject("MSXML2.XMLHTTP");}
    else if (window.createRequest)
         {oHttpReq = window.createRequest();}
    else
         {oHttpReq = new XMLHttpRequest();}
    return oHttpReq;
}

注：escape()避免了后台获得前台页面值的乱码问题。