我正在获取RangeError [ERR_HTTP_INVALID_STATUS_CODE]：无效状态代码:未定义

const http = require('http');

const server = http.createServer((req, res) => {
  if (req.url === '/') {
    res.statusCode = 200;
    res.setHeader('Content-Type', 'text/plain');
    res.end('Hello World\n');
  } else {
    res.statusCode = 404;
    res.end('Not Found\n');
  }
});

server.listen(3000, () => {
  console.log('Server running at http://localhost:3000/');
});

const express = require('express');
const app = express();

app.get('/', (req, res) => {
  res.status(200).send('Hello World');
});

app.use((req, res) => {
  res.status(404).send('Not Found');
});

app.listen(3000, () => {
  console.log('Server running at http://localhost:3000/');
});

const express = require('express');
const app = express();

app.get('/', (req, res) => {
  res.status(200).send('Hello World');
});

app.get('/not-found', (req, res) => {
  res.status(404).send('Not Found');
});

app.use((req, res) => {
  res.status(404).send('Not Found');
});

app.listen(3000, () => {
  console.log('Server running at http://localhost:3000/');
});