js+ajax解决跨域请求

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

app.use((req, res, next) => {
  res.header('Access-Control-Allow-Origin', '*'); // 允许所有源，也可以指定特定源
  res.header('Access-Control-Allow-Methods', 'GET, POST, PUT, DELETE, OPTIONS');
  res.header('Access-Control-Allow-Headers', 'Content-Type, Authorization');
  next();
});

app.get('/data', (req, res) => {
  res.json({ message: 'This is data from the server.' });
});

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

function fetchData() {
  fetch('http://example.com/data')
    .then(response => response.json())
    .then(data => console.log(data))
    .catch(error => console.error('Error:', error));
}

fetchData();

app.get('/data', (req, res) => {
  const data = { message: 'This is data from the server.' };
  const callback = req.query.callback;
  res.send(`${callback}(${JSON.stringify(data)})`);
});

<script>
function handleResponse(data) {
  console.log(data);
}
</script>
<script src="http://example.com/data?callback=handleResponse"></script>