App.js

import React, { useState, useEffect } from "react";
import { BrowserRouter, Switch, Route, Link } from "react-router-dom";

function Config({}) {
  return (
    <div className="config">
      <h1>Config</h1>
      <Link to="/">Todos</Link>
    </div>
  );
}

function Todos({}) {
  return (
    <div className="todos">
      <h1>Todos</h1>
      <Link to="/config">Config</Link>
    </div>
  );
}

function App({}) {
  return (
    <div className="app">
      <BrowserRouter>
        <Switch>
          <Route path="/config" render={props => <Config {...props} />} />
          <Route path="/" render={props => <Todos {...props} />} />
        </Switch>
      </BrowserRouter>
    </div>
  );
}

export default App;