如果我输入了错误的路线，如何在Node.js中显示“404Not found”？

const http = require('http');
const url = require('url');
const fs = require('fs');

http.createServer((req, res) => {
  // 解析请求的URL
  const pathName = url.parse(req.url).pathname;
  
  // 判断请求的路由
  if (pathName === '/') {
    // 处理根路由
    res.writeHead(200, {'Content-Type': 'text/html'});
    res.write('<h1>Welcome to the homepage!</h1>');
    res.end();
  } else {
    // 其他路由都显示"404 Not Found"
    res.writeHead(404, {'Content-Type': 'text/html'});
    res.write('<h1>404 Not Found</h1>');
    res.end();
  }
}).listen(3000, () => {
  console.log('Server is running on port 3000');
});