vue项目中使用fetch的实现方法

/** 
* baseUrl: 域名地址 
* routerMode: 路由模式
*/

let baseUrl = '';
let routerMode = 'history';
if (process.env.NODE_ENV == 'development') { 
  baseUrl = 'http://localhost:3000';
}else{ 
  baseUrl = 'http://xxxx这里是线上地址xxx';
}

export { baseUrl, routerMode }

import { baseUrl } from './env'
export default async(url = '', data = {}, type = 'GET', method = 'fetch') => {
 type = type.toUpperCase();
 url = baseUrl + url;

    // 此处规定get请求的参数使用时放在data中，如同post请求
 if (type == 'GET') {
 let dataStr = ''; 
 Object.keys(data).forEach(key => {
  dataStr += key + '=' + data[key] + '&';
 })
 
 if (dataStr !== '') {
  dataStr = dataStr.substr(0, dataStr.lastIndexOf('&'));
  url = url + '?' + dataStr;
 }
 }

    // 对于支持fetch方法的浏览器，处理如下：
 if (window.fetch && method == 'fetch') {
 let requestConfig = {
            // fetch默认不会带cookie，需要添加配置项credentials允许携带cookie
  credentials: 'include', 
  method: type,
  headers: {
  'Accept': 'application/json',
  'Content-Type': 'application/json'
  },
  mode: "cors", // 以CORS的形式跨域
  cache: "force-cache"
 }
 
 if (type == 'POST') {
  Object.defineProperty(requestConfig, 'body', {
  value: JSON.stringify(data)
  })
 }
 
 try {
  const response = await fetch(url, requestConfig);
  const responseJson = await response.json();
  return responseJson
 } catch (error) {
  throw new Error(error)
 }
 } else { // 对于不支持fetch的浏览器，便自动使用 ajax + promise
 return new Promise((resolve, reject) => {
  let requestObj;
  if (window.XMLHttpRequest) {
  requestObj = new XMLHttpRequest();
  } else {
  requestObj = new ActiveXObject; // 兼容IE
  }
 
  let sendData = '';
  if (type == 'POST') {
  sendData = JSON.stringify(data);
  }
 
  requestObj.open(type, url, true);
  requestObj.setRequestHeader("Content-type", "application/x-www-form-urlencoded");
  requestObj.send(sendData);
 
  requestObj.onreadystatechange = () => {
  if (requestObj.readyState == 4) {
   if (requestObj.status == 200) {
   let obj = requestObj.response
   if (typeof obj !== 'object') {
    obj = JSON.parse(obj);
   }
   resolve(obj)
   } else {
   reject(requestObj)
   }
  }
  }
 })
 }
}