Ajax之三：结果分类

中的x指的是XML，早期的数据格式都喜欢用XML，然后一层层的解析。当然简单的也会返回HTML(或称HTML片段)。
现在使用ON格式的也很多。根据不同需求，给Ajax对象添加了三个实用方法：Ajax.text、Ajax.json、Ajax.xml。

Ajax.text返回纯文本，即responseText

Ajax.json返回json，即会将responseText解析成js对象

Ajax.xml返回xml文档，即responseXML

使用方式与Ajax.request相同，第一个参数是请求url，第二个是配置参数。

完整代码

01  Ajax =
02  function(){
03      function request(url,opt){
04          function fn(){}
05          var async   = opt.async !== false,
06              method  = opt.method    || 'GET',
07              type    = opt.type      || 'text',
08              encode  = opt.encode    || 'UTF-8',
09              data    = opt.data      || null,
10              success = opt.success   || fn,
11              failure = opt.failure   || fn;
12              method  = method.toUpperCase();
13          if(data && typeof data == 'object'){//对象转换成字符串键值对
14              data = _serialize(data);
15          }
16          if(method == 'GET' && data){
17              url += (url.indexOf('?') == -1 ? '?' : '&') + data;
18              data = null;
19          }  
20          var xhr = window.XMLHttpRequest ? new XMLHttpRequest() : new ActiveXObject('Microsoft.XMLHTTP');
21          xhr.onreadystatechange = function(){
22              _onStateChange(xhr,type,success,failure);
23          };
24          xhr.open(method,url,async);
25          if(method == 'POST'){
26              xhr.setRequestHeader('Content-type', 'application/x-www-form-urlencoded;charset=' + encode);
27          }
28          xhr.send(data);
29          return xhr;
30      }
31      function _serialize(obj){
32          var a = [];
33          for(var k in obj){
34              var val = obj[k];
35              if(val.constructor == Array){
36                  for(var i=0,len=val.length;i<len;i++){
37                      a.push(k + '=' + encodeURIComponent(val[i]));
38                  }              
39              }else{
40                  a.push(k + '=' + encodeURIComponent(val));
41              }              
42          }
43          return a.join('&');
44      }
45      function _onStateChange(xhr,type,success,failure){
46          if(xhr.readyState == 4){
47              var s = xhr.status, result;
48              if(s>= 200 && s < 300){
49                  switch(type){
50                      case 'text':
51                          result = xhr.responseText;
52                          break;
53                      case 'json':
54                          result = function(str){
55                              return (new Function('return ' + str))();
56                          }(xhr.responseText);
57                          break;
58                      case 'xml':
59                          result = xhr.responseXML;
60                          break;
61                  }
62                  success(result);   
63              }else{
64                  failure(xhr);
65              }
66          }else{}
67      }
68      return (function(){
69          var Ajax = {request:request}, types = ['text','json','xml'];
70          for(var i=0,len=types.length;i<len;i++){
71              Ajax[types[i]] = function(i){
72                  return function(url,opt){
73                      opt = opt || {};
74                      opt.type = types[i];
75                      return request(url,opt);
76                  };
77              }(i);
78          }
79          return Ajax;
80      })();
81  }();