老司機(jī)你好，感謝您來幫助

● 問題1：請看這第4行，能打印出來。為什么第5行打出出來是undefind？
（在調(diào)試時(shí)還是顯示有數(shù)據(jù)，這不是奇怪嗎？）
● 這個(gè)參數(shù)是不是Rreact-router 這個(gè)路由傳給它的？
▼下面是代碼的片段

import React from 'react'
import { BrowserRouter, Route, Link } from 'react-router-dom';
import './App.css';
import Home from './page01/Home.js'
import About from './page01/About.js'
import Topics from './page01/Topics.js'

const App = () => (
    <BrowserRouter  >
        <div>
            <nav>
                <ul>
                    <li><Link to="/">首頁</Link></li>
                    <li><Link to="/about">關(guān)于</Link></li>
                    <li><Link to="/topics">主題列表</Link></li>
                </ul>
            </nav>    
            <main>
                <Route exact path="/" component={Home}/>
                <Route path="/about" component={About}/>{*/?就這個(gè)組件/*}
                <Route path="/topics" component={Topics}/>
            </main>
        </div>
    </BrowserRouter>
)

export default App

-

import React from 'react';
//▼看就下面5行打出不來，4行可以打印出來
const About = ({ match }) => {
    console.log(match);
    console.log(arguments[0].match);
    return <h2>關(guān)于</h2>    
}
export default About