SyntaxError:在reactjs中执行api post请求时，位置0处的意外标记<

fetch('https://example.com/api/data', {
  method: 'POST',
  headers: {
    'Content-Type': 'application/json'
  },
  body: JSON.stringify({ key: 'value' })
})
.then(response => {
  if (!response.ok) {
    throw new Error('Network response was not ok ' + response.statusText);
  }
  return response.json();
})
.then(data => console.log(data))
.catch(error => console.error('There was a problem with the fetch operation:', error));

fetch('https://example.com/api/data', {
  method: 'POST',
  headers: {
    'Content-Type': 'application/json'
  },
  body: JSON.stringify({ key: 'value' })
})
.then(response => response.json())
.then(data => console.log(data))
.catch(error => console.error('Error:', error));

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

app.use(cors());

app.post('/api/data', (req, res) => {
  res.json({ message: 'Data received' });
});

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