JSON学习demo2（httprequest篇）

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<!DOCTYPE html> <html> <head>     <meta charset="UTF-8">     <title>ajax学习_http_request</title>      <script>         //1.HttpRequest初始化,判断浏览器类型         var request = null;         var checkUserName = function(){               if(window.XMLHttpRequest()){    //火狐，苹果                    request = new XMLHttpRequest();               }else if(window.ActiveXObject()){  //IE                    request = new ActiveXObject("Microsoft.XMLHTTP");               }             //2.通过对象打开请求              if(request){                  request.open("GET","user.json",true);    //true代表服务器返回时间内是否执行以下的代码                  request.send(null);                    //3.发送请求                  request.onreadystatechange = callBack;              }         }          function callBack(){             if(request.readyState == 4){                      if(request.status == 0){                          var response = request.responseText;                          var user = eval("("+response+")").group;                          for(var i=0; i<=user.length; i++){                               console.log("name="+user[i].name+"  age="+user[i].age);                           }                       }              }         }           </script> </head>   <body> <table border="1">     <tr>         <td>用户名：</td>         <td><input type="text" id="username" onblur="checkUserName()"></td>      </tr> </table> <span id="showMessage"></span> </body> </html>

json文件内容：

{    "group" : [        {"name": "justin" , "age": "20"},        {"name": "Jan" , "age": "22"},        {"name": "Boss" , "age": "30"}    ] }