原生JS封装ajax函数

 1 function ajax(params) {
 2     params.data = params.data || "";
 3     params.type = params.type || "get";
 4     if(!params.url) {
 5         throw new Error("未指定连接");
 6     }
 7     params.async = params.async || true;
 8     var xhr;
 9     //兼容IE
10     if(window.VBArray) {
11         xhr = new ActiveXObject("Msxml2.XMLHTTP");
12     } else {
13         xhr = new XMLHttpRequest();
14     }
15     xhr.open(params.type, params.url, params.sync);
16     //处理回调函数
17     xhr.onreadystatechange = function() {
18         console.log(xhr.status);
19         if(xhr.status == 200) {
20             if(xhr.readyState == 4) {
21                 params.success ? params.success(xhr.responseText) : "";
22             }
23         } else {
24             throw new Error("请求失败，状态码：" + xhr.status);
25         }
26     }
27     if(params.type == "get") {
28         xhr.send();
29     } else {
30         xhr.setRequestHeader("Content-type", "application/x-www-form-urlencoded");
31         xhr.send(params.data);
32     }
33 }

                ajax({
                    type:"get",
                    url:"http://localhost:8080/AJAX_test/txt/pbl.lol",
                    success:function(msg){
                        var list = JSON.parse(msg);
                    }
                })