Como postar dados no banco de dados usando a API Fetch no React.js

handleSubmit (event) {
  //alert('A list was submitted: ' + this.state.formvalue);
  event.preventDefault();
  fetch('your post url here', {
    method: 'POST',
    headers: {
      'Accept': 'application/json',
      'Content-Type': 'application/json'
    },
    body: JSON.stringify({
      id: this.state.id,
      item: this.state.item,
      itemType: this.state.itemType
    })
  })
  .then(res => res.json())
  .then(data => console.log(data))
  .catch(err => console.log(err);
}

app.post('/api/listitems', (req, res) => {
  var postData  = req.body;
  connection.query('INSERT INTO list_items SET ?', postData, (error, results, fields) => {
    if (error) throw error;
    res.end(JSON.stringify(results));
  });
});