Ajax的简单用例

<% @ Page Language = " VB "  AutoEventWireup = " false "  CodeFile = " Default.aspx.vb "  Inherits = " _Default "   %>

<! DOCTYPE html PUBLIC  " -//W3C//DTD XHTML 1.0 Transitional//EN "   " http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd " >

< html xmlns = " http://www.w3.org/1999/xhtml "   >
< head runat = " server " >
     < title > Untitled Page </ title >
     < link href = " StyleSheet.css "  rel = " stylesheet "  type = " text/css "   />
     < script language = " javascript "  type = " text/jscript " >
         // 检测浏览器,创建xmlhttp-request对象
        function getXMLRequester()
         ... {
            var xmlhttp_request = false;
            try
            ...{
                if(window.ActiveXObject)
                ...{
                    for(var i = 5;i;i--)
                    ...{
                        try
                        ...{
                            if(i==2)
                            ...{
                                xmlhttp_request = new ActiveXObject("Microsoft.XMLHTTP");
                            }
                            else
                            ...{
                                xmlhttp_request = new ActiveXObject("Msxml2.XMLHTTP" +i+"0");
                                xmlhttp_request.setRequestHeader("Content-Type","text-xml");
                                xmlhttp_request.setRequestHeader("Content_Type","gb2312");                                
                            }
                            break;
                        }
                        catch(e)
                        ...{
                            xmlhttp_request=false;
                        }
                    }
                }
                else if(window.XMLHttpRequest)
                ...{
                    xmlhttp_request = new XMLHttpRequest();
                    if(xmlhttp_request.overrideMineType)
                    ...{
                        xmlhttp_request.overrideMineType("text/xml");
                    }
                }
            }
            catch(e)
            ...{
                xmlhttp_request = false;
            }
            return xmlhttp_request;
        }
        
        function IDRequest(n)
         ... {
            url = n + document.getElementById("txtUserID").value;//定义网址参数
            
            xmlhttp_request = getXMLRequester();
            xmlhttp_request.onreadystatechange = doContents;//调用doContent函数;
            xmlhttp_request.open("Get",url,true);
            
            xmlhttp_request.send(null);
        }
        
        function doContents()
         ... {
            if(xmlhttp_request.readyState == 4)//收到完整的服务器响应
            ...{
                if(xmlhttp_request.status == 200)//Http服务器响应ok
                    document.getElementById("message").innerHTML = xmlhttp_request.responseText;//服务器响应的值
                else
                    alert(http_request.status);
            }
        }
</ script >
</ head >
< body >
     < form id = " form1 "  runat = " server " >
     < div >
         < input type = " text "  id = " txtUserID "  style = " font-size:12px; "   />
         < input type = " button "  id = " btnOk "  value = " 校验 "  style = " font-size:12px "  onclick  = " IDRequest('http://reg.163.com/register/checkssn.jsp?username=') "   />
         < div id = " message " ></ div >
     </ div >
     </ form >
</ body >
</ html >