Fetch explained

fetch.js

function addUser(details) {
  return fetch('https://api.example.com/user', {
    mode: 'cors',
    method: 'POST',
    credentials: 'include',
    body: JSON.stringify(details),
    headers: {
      'Content-Type': 'application/json',
      'Accept': 'application/json',
      'X-XSRF-TOKEN': getCookieValue('XSRF-TOKEN')
    }
  }).then(response => {
    return response.json().then(data => {
      if (response.ok) {
        return data;
      } else {
        return Promise.reject({ status: response.status, data });
      }
    });
  });
}