Ajax：一种网页开发技术(Asynchronous Javascript + XML)

1. 创建新的 XMLHttpRequest 对象(Ajax 应用程序的核心):
   

   <script language="javascript" type="text/javascript">var xmlHttp = new XMLHttpRequest();
   </script>

2. 用 JavaScript 代码捕获和设置字段值

   //获取 id 值为 first_name 的表单域
   var name = document.getElementById('first_name').value;//修改 id 值为 test 的表单域的值
   document.getElementById('test').value = response[0];
   

   　　

3. 在 Microsoft 浏览器上创建 XMLHttpRequest 对象

   var xmlHttp = false;
   try {xmlHttp = new ActiveXObject("Msxml2.XMLHTTP");
   } catch (e) {try {xmlHttp = new ActiveXObject("Microsoft.XMLHTTP");} catch (e2) {xmlHttp = false;}
   }
   

   　　

4. 以支持多种浏览器的方式创建 XMLHttpRequest 对象

   /* Create a new XMLHttpRequest object to talk to the Web server */
   var xmlHttp = false;
   /*@cc_on @*/
   /*@if (@_jscript_version >= 5)
   try {xmlHttp = new ActiveXObject("Msxml2.XMLHTTP");
   } catch (e) {try {xmlHttp = new ActiveXObject("Microsoft.XMLHTTP");} catch (e2) {xmlHttp = false;}
   }
   @end @*/if (!xmlHttp && typeof XMLHttpRequest != 'undefined') {xmlHttp = new XMLHttpRequest();
   }
   

   　　

5. 开始工作：发送Ajax请求

   function callServer() {// Get the city and state from the web formvar city   = document.getElementById("city").value;var state = document.getElementById("state").value;// Build the URL to connect tovar url = "/scripts/getZipCode.php?city=" + escape(city) + "&state=" + escape(state);// Open a connection to the serverxmlHttp.open("GET", url, true);// Setup a function for the server to run when it's donexmlHttp.onreadystatechange = updatePage;// Send the requestxmlHttp.send(null);
   }