老是提示“无法解析json字符串”！帮个忙，大侠们PhoneGap+js

 {
     xtype: 'button',
     text: '恢复名片',
     ui: 'action',
     listeners: {
     'tap':function(){
     379
         //申明一个数组
var contacts = ['download','demo','pass',[]];

var x = Ext.util.JSON.encode(contacts);

        Ext.Ajax.request({
            url: "http://192.168.3.101:8080/contacts/contacts",    
            method: "POST",
            jsonData : x,
            
            //请求成功的回调函数 
            success: function(response, opts) {
             console.log('success');
console.log(response);
             console.log(response.responseText);
                                             ————————这里出错！无法解析json
             var responseMs = Ext.util.JSON.decode(response.responseText); 
            
             console.log(responseMs);
            }, 
            
            failure: function() {
              // 请求失败的回调函数
             alert("获取目录请求失败！");
            }
        });
     }
     }