It worked well yesterday, but today localhost:3000 doesn't show me anything in browser all of sudden.

### App.js

```
import React, { useEffect }from 'react'
import { BrowserRouter as Router, Route, Switch } from "react-router-dom";
import {connect} from 'react-redux'
import * as auth_actions from './store/actions/auth_action'

import Home from './Authentication/Home'
import Login from './Authentication/Login'
import Signup from './Authentication/Signup'
import Loading from './Authentication/Loading'
import Activate from './Authentication/Activate'
import PasswordReset from './Authentication/PasswordReset'
import PasswordResetConfirm from './Authentication/PasswordResetConfirm'

import Cards from './Swipe/Cards'
import Match from './Swipe/Match'

import Setting from './Setting/Setting'
import Editor from './Setting/Editor'
import Chat from './Chat/Chat'
import ChatPanels from './Chat/ChatPanels'

const App = (props) => {

    useEffect(() => {
        props.checkAuthenticated();
    })

        return(
            <Router>
              <Switch>
                    <Route exact path='/' component={Home} />
                    <Route exact path='/login' component={Login} />
                    <Route exact path='/signup' component={Signup} />
                    <Route exact path='/reset_password' component={PasswordReset} />
                    <Route exact path='/password/reset/confirm/:uid/:token' component={PasswordResetConfirm} />
                    <Route exact path='/loading' component={Loading}/>
                    <Route exact path='/activate/:uid/:token' component={Activate} />
                    <Route exact path="/chat/:friend/:ChatID" component={Chat}/>
                    <Route exact path='/swipe' component={Cards}/>
                    <Route exact path='/setting' component={Setting}/>
                    <Route exact path='/chatpanel' component={ChatPanels}/>
                    <Route exact path='/edit' component={Editor}/>
                    <Route exact path='/match' component={Match}/>
              </Switch>
            </Router>
        );
}

const mapDispatchToProps = dispatch => {
    return {
        checkAuthenticated: () => dispatch(auth_actions.checkAuthenticated)
    }
}

export default connect(null, mapDispatchToProps)(App)

```

### index.js

```
import ReactDOM from 'react-dom';
import React from 'react'
import { createStore, applyMiddleware } from 'redux';
import { Provider } from 'react-redux';
import 'antd/dist/antd.css';
import reducer from './store/reducers/index';
import App from './App';
import { composeWithDevTools } from "redux-devtools-extension";
import thunk from 'redux-thunk';

const initialState = {}
const middelware = [thunk]
const store = createStore(
    reducer,
    initialState,
    composeWithDevTools(applyMiddleware(...middelware))
)

const app = 
    <Provider store={store}>
        <App />
    </Provider>

ReactDOM.render(app, document.getElementById("root"));

```

### index.html

```
.
.
.
<title>Speak Up</title>
  </head>
  <body>
    <div id="root" style="width:100%"></div>
    <script src="bundle.js" type="text/javascript"></script>
.
.
.
</body>

```

when I save the code, no errors comes up. In browser, no error messages appears. Before this happened, there were error messages that I expected, and I tried to fix them, but when I debug, It came up. Are there some reasons why this happened?
Could you tell me how to fix it?

Thank you:)