js中发送请求400错误

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

app.get('/user', (req, res) => {
  const username = req.query.username;
  
  if (!username || !/^\w+([-+.]\w+)*@\w+([-.]\w+)*\.\w+([-.]\w+)*$/.test(username)) {
    return res.status(400).send('Invalid username format');
  }
  
  // 处理合法请求...
  res.send(`Hello, ${username}!`);
});

app.listen(3000, () => console.log('Server running on port 3000'));

fetch('/user?username=test@example.com')
  .then(response => {
    if (!response.ok) {
      throw new Error(`HTTP error! status: ${response.status}`);
    }
    return response.text();
  })
  .then(data => console.log(data))
  .catch(error => console.error('Error:', error));