react中在刷新页面时提示

在入口文件index.js文件中加入红色段：
 

import 'antd/dist/antd.css';
import './assets/css/ant-cus.css'
import './assets/css/base.css'
import './assets/css/index.css'
import './assets/css/header.css'
import './assets/css/rightClick.css'
import './assets/css/recycle.css'
import './assets/css/imgPreview.css'
import React from 'react';
import ReactDOM from 'react-dom';
import * as serviceWorker from './serviceWorker';
import CommonUtil from './util/CommonUtil';
import ApiUtil from './util/ApiUtil';
import { HashRouter, Switch } from 'react-router-dom';
import FrontendAuth from './frontendAuth';
import routerMap from './routerMap';React.api = ApiUtil.getInstance(React);
React.util = CommonUtil.getInstance(React);window.onbeforeunload = function (e) {if (localStorage.getItem("isUpload") === 'yes') { //刷新时提示的条件localStorage.setItem("isUpload", 'no');const dialogText = "重新加载网页，系统可能不会保存您做的更改";e.returnValue = dialogText;return dialogText;}
};ReactDOM.render(<div className="mt-yp-app"><HashRouter><Switch><FrontendAuth routerConfig={routerMap} /></Switch></HashRouter></div>,document.getElementById('mt-yp')
);
serviceWorker.unregister();