封装一个基于axios的 Ajax

/* index.js */
        /* GET请求 */
       function testGet() {
           axios({
            url:'http://localhost:3000/posts',
            method:'GET',
            params:{
                id:2,
                xxx:"abc"
            }
           }).then(response=>{
               console.log(response);
               
           },error=>{
               console.log(error.message);
               
           })
       }
       /* Post请求 */
       function testPost() {
           axios({
               url:'http://localhost:3000/posts',
               method:'POST',
               data:{
                "title": "json-server----","author": "typicode----"
               }
           }).then(response=>{
               console.log(response);
               
           },error=>{
               console.log(error.message);
           })
       }
       /* PUT请求 */
       function testPut() {
           axios({
               url:'http://localhost:3000/posts/2',
               method:'PUT',
               data:{
                "title": "json-server666","author": "typicode666"
               }
           }).then(response=>{
               console.log(response);
               
           },error=>{
               console.log(error.message);
           })
       }
       /* Delete请求 */
       function testDelete() {
           axios({
               url:'http://localhost:3000/posts/6',
               method:'DELETE',
               data:{
                "title": "json-server----","author": "typicode----"
               }
           }).then(response=>{
               console.log(response);
               
           },error=>{
               console.log(error.message);
           })
       }

       /* 封装一个ajax基于axios */
        function axios({
            url,
            method,
            params={},
            data={}
        }) {
            // 返回一个promise对象
            return new Promise((resolve,reject)=>{

                // 处理method 转换为大写
                method = method.toUpperCase()

                let queryString = ''// 处理query参数(拼接到url上) id=1&xxx=abc
                Object.keys(params).forEach(v=>{
                    queryString+=`${v}=${params[v]}&`
                })
                if(queryString){
                    queryString = queryString.substring(0,queryString.length-1)
                    url += '?' + queryString
                }

                // 1. 执行异步ajax请求
                const request = new XMLHttpRequest()// 1.1. 创建xhr对象
                request.open(method,url,true)// 1.2. 打开链接(初始化请求, 没有请求)
                // 1.3. 发送请求
                if(method==='GET'||method==='DELETE'){
                    request.send()
                }else if(method==='POST'||method==='PUT'){
                    request.setRequestHeader('Content-Type','application/json;charset=utf-8')// 告诉服务器请求体的格式是json
                    request.send(JSON.stringify(data)) // 发送json格式请求体参数
                }
                // 1.4  绑定状态改变的监听
                request.onreadystatechange = function(){
                    // 如果请求没有完成, 直接结束
                    if(request.readyState!==4){
                        return
                    }
                    // 如果响应状态码在[200,300)之间代表成功, 否则失败
                    const {status,statusText} = request
                    // 2.  如果调用成功了, 调用 resolve
                    if(status>=200 && status<=299){
                        // 准备结果数据对象response
                        const response = {
                            data:JSON.parse(request.response),// 响应体(装换为json格式)
                            status,// 响应状态码
                            statusText// 响应文本
                        }
                        resolve(response)
                    }else{ // 3.  如果调用失败了, 调用 reject
                        reject(new Error('request error status' + status))
                    }
                }
            })
        }