aja 笔记1

   <script type="text/javascript">
            function check(){
                var account=document.loginForm.account.value
                var pwd=document.loginForm.password.value
               var xmlHttp;
            if (window.XMLHttpRequest){
          
               xmlHttp = new XMLHttpRequest();
            }else if (window.ActiveXObject){
              xmlHttp = new ActiveXObject("Microsoft.XMLHTTP");
            
              }
              xmlHttp.open("post","ajax.jsp?account="+account+"&password="+pwd,true);
       
              xmlHttp.onreadystatechange=function(){
            
              if(xmlHttp.readyState==4){
                xm.innerHTML=xmlHttp.responseText
                }else{
              
                xm.innerHTML="正在登录，请稍等..."
                }
              }          
             xmlHttp.send();
  
            }
          
              
  </script>
   <form name="loginForm">
    姓名<input type="text" name="account" ><BR>
  
    密码<input type="password" name="password"><BR>
  
    <input type="button" value="OK" onclick="check()">

</form>
<hr>
<span id="xm"></span>
</body>

ajax.jsp内容

<%
  String account= request.getParameter("account");
  String pwd= request.getParameter("password");
  if(account.equals(pwd)){
     out.println("登录成功");
  }
  else{
  out.println("登录失败");
  }

%>
XMLHTTPRequest对象什么是
mlHttp是一套可以在Javascript、VbScript、Jscript等脚本语言中通过http协议传送或从接收 XML及其他数据的一套API。XmlHttp最大的用处是可以更新网页的部分内容而不需要刷新整个页面
属性：
Property Name Type/Description  
onreadystatechange Callback function; set this to a function that will be called whenever readyState changes.  
readyState Number; 0 means uninitialized, open() has not yet been called; 1 means loading, send() has not been called; 2 means loaded, send() has been called and headers/status are available; 3 interactive, responseText holds partial data; 4 means completed.  
responseText string; the plain text of the response.  
responseXML DOM Document object; an XML return value.  
status Response status code, such as 200 (Okay) or 404 (Not Found).  
statusText string; the text associated with the HTTP response status.