学步园

这几天被xmlHttpRequest缓存折腾的挺郁闷，第一次用Ajax做一个定时刷新的东西，结果每次返回值都和第一次一样，考虑到应该是缓存搞的鬼，然后经人指点，在url后面加一个随机数就可以解决了，因为只要url不一样js就认为是一个新的请求，不会读缓存了
原始代码如下：

            //创建一个xmlHttpRequest对象
            function createXMLHttpRequest()
            {
            var xmlHttp;//定义xmlHttp
                if(window.ActiveXObject)
                {
                    xmlHttp = new ActiveXObject("Microsoft.XMLHTTP");
                }
                else if(window.XMLHttpRequest)
                {
                    xmlHttp = new XMLHttpRequest();
                }
                return xmlHttp;
            }
            
            function Refresh()
            {
                var xmlHttp = createXMLHttpRequest();
                var url= "NewMessageAlertHandler.aspx";
                xmlHttp.open("GET",url,true);
                xmlHttp.onreadystatechange=function(){
                if(xmlHttp.readyState==4 || xmlHttp.readyState=="complete")
                {
                    if(xmlHttp.status==200)
                    {
                        //alert(xmlHttp.responseText);
                        document.getElementById("divImg").style.display=xmlHttp.responseText;
                        xmlHttp = null;
                        setTimeout("Refresh()",5000);
                        
                    }
                }
                
                };
                xmlHttp.send(null);
                
            }

改进之后的代码如下

            //创建一个xmlHttpRequest对象
            function createXMLHttpRequest()
            {
            var xmlHttp;//定义xmlHttp
                if(window.ActiveXObject)
                {
                    xmlHttp = new ActiveXObject("Microsoft.XMLHTTP");
                }
                else if(window.XMLHttpRequest)
                {
                    xmlHttp = new XMLHttpRequest();
                }
                return xmlHttp;
            }
            
            function Refresh()
            {
                var xmlHttp = createXMLHttpRequest();
                var nowTime = new Date().getTime();//获取当前时间作为随机数
                var url= "NewMessageAlertHandler.aspx?time="+nowTime;
                xmlHttp.open("GET",url,true);
                xmlHttp.onreadystatechange=function(){
                if(xmlHttp.readyState==4 || xmlHttp.readyState=="complete")
                {
                    if(xmlHttp.status==200)
                    {
                        //alert(xmlHttp.responseText);
                        document.getElementById("divImg").style.display=xmlHttp.responseText;
                        xmlHttp = null;
                        setTimeout("Refresh()",5000);
                        
                    }
                }
                
                };
                xmlHttp.send(null);
                
            }