async function callApi(url, method = 'GET', data = null, token = null) {
  const headers = {
    'Content-Type': 'application/json'
  };

  if (token) {
    headers['Authorization'] = `Bearer ${token}`;
  }

  const options = {
    method: method,
    headers: headers
  };

  if (data && (method === 'POST' || method === 'PUT' || method === 'PATCH')) {
    options.body = JSON.stringify(data);
  }

  try {
    const response = await fetch(url, options);
    if (!response.ok) {
      const errorData = await response.json();
      throw new Error(`HTTP error! status: ${response.status}, message: ${errorData.message || response.statusText}`);
    }
    return await response.json();
  } catch (error) {
    console.error('API call failed:', error);
    throw error;
  }
}

// Example Usage:
// const authToken = 'your_jwt_token';
//
// // GET request
// callApi('https://api.example.com/items', 'GET', null, authToken)
//   .then(data => console.log('GET Data:', data))
//   .catch(err => console.error('GET Error:', err));
//
// // POST request
// const newItem = { name: 'New Item', description: 'This is a new item.' };
// callApi('https://api.example.com/items', 'POST', newItem, authToken)
//   .then(data => console.log('POST Data:', data))
//   .catch(err => console.error('POST Error:', err));