原生ajax方法

 1 function ajax(options){
 2     options = options || {};
 3     var method = (options.type || "GET").toupperCase(),
 4         url = options.url,
 5         queryString = null;
 6     if(!url)
 7         return;
 8     if(options.data){
 9         queryString = [];
10         for(var attr in options.data){
11         queryString.push(attr + "=" +options.data[attr]);
12         }
13         queryString = queryString.join("&");
14     }
15     if(method === "GET" && queryString){
16         url += "?"+queryString;
17         queryString = "";
18     }
19     var xhr = new XMLHttpRequest();
20     xhr.open(method,url,true);
21     if(method === "POST")
22         xhr.setRequestHeader("Content-Type", "application/x-www-form-urlencoded");
23     xhr.send(queryString);
24     xhr.onreadystatechange = function(){
25         if(xhr.readyState === 4){
26         if(xhr.status === 200){
27             var data = xhr.responseText;
28             if(options.dataType === "json")
29             data = JSON.parse(data);
30             options.success && options.success(data);
31         }else{
32             options.error && options.error(xhr.status);
33         }
34         }
35     }
36 }