TypeError：无法读取未定义的react和material ui的属性“ root”

Question

我使用： ” @ material-ui / core“：” ^ 4.1.1“， “ react”：“ ^ 16.8.6”， “ react-dom”：“ ^ 16.8.6”， 我只是试图渲染一个按钮，并在帖子标题中得到错误

我尝试安装npm对等依赖项

import React, { Component } from "react";
import Link from "@material-ui/core/Link";

class Welcome extends Component {
  render() {
    return (
      <div className="Welcome">
        <p>This is your public-facing component.</p>
        <Link
          component="button"
          variant="body2"
          onClick={() => {
            alert("I'm a button.");
          }}
        >
          Button Link
        </Link>
      </div>
    );
  }
}
export default Welcome;

我应该看到链接

调用上述组件的代码

import { BrowserRouter, Route, Link } from 'react-router-dom';
import Welcome from './Welcome';
import Secured from './Secured';
import Logout from './Logout';
import './App.css';

class App extends Component {

  render() {
    return (
      <BrowserRouter>
        <div className="container">
          <ul>
            <li><Link to="/">public component</Link></li>
            <li><Link to="/secured">secured component</Link></li>
          </ul>
          <Route exact path="/" component={Welcome} />
          <Route path="/secured" component={Secured} />
        </div>
      </BrowserRouter>
    );
  }
}
export default App;

import React from 'react';
import ReactDOM from 'react-dom';
import './index.css';
import App from './App';
import * as serviceWorker from './serviceWorker';

ReactDOM.render(<App />, document.getElementById('root'));