default function to send and and load data from server

ajaxData.js

// Example POST method implementation:
// ajaxData(`http://example.com/answer`, {answer: 42})
//   .then(data => console.log(JSON.stringify(data))) // JSON-string from `response.json()` call
//   .catch(error => console.error(error));

function getCookie(name) {
  let cookieValue = null;
  if (document.cookie && document.cookie !== '') {
    const cookies = document.cookie.split(';');
    for (let i = 0; i < cookies.length; i += 1) {
      const cookie = cookies[i].trim();
      // Does this cookie string begin with the name we want?
      if (cookie.substring(0, name.length + 1) === `${name}=`) {
        cookieValue = decodeURIComponent(cookie.substring(name.length + 1));
        break;
      }
    }
  }
  return cookieValue;
}

function queryParams(params) {
  return Object.keys(params)
    .map(k => `${encodeURIComponent(k)}=${encodeURIComponent(params[k])}`)
    .join('&');
}

export const ajaxData = function(url = '', data = {}, method = 'POST') {
  // Default options are marked with *
  const bareToken = localStorage.getItem('token');
  const baseAuth = localStorage.getItem('baseAuth');
  const csrfToken = getCookie('csrftoken');

  // add headers
  const baseHeaders = new Headers();
  baseHeaders.append('Content-Type', 'application/json; charset=utf-8');
  baseHeaders.append('Accept', 'application/json');

  if (csrfToken) {
    baseHeaders.append('X-CSRFToken', csrfToken);
  }

  // try use baseAuth by default
  if (!baseAuth) {
    baseHeaders.append('Authorization', `Token ${bareToken}`);
  } else {
    baseHeaders.append('Authorization', `Basic ${baseAuth}`);
  }

  const requestData = {
    method, // *GET, POST, PUT, DELETE, etc.
    mode: 'cors', // no-cors, cors, *same-origin
    cache: 'no-cache', // *default, no-cache, reload, force-cache, only-if-cached
    credentials: 'same-origin', // include, same-origin, *omit
    headers: baseHeaders,
    redirect: 'follow', // manual, *follow, error
    referrer: 'no-referrer', // no-referrer, *client
    body: JSON.stringify(data), // body data type must match "Content-Type" header
  };

  if (data === {}) {
    delete requestData.body;
  }

  if (['GET'].indexOf(method) > -1) {
    url += `?${queryParams(data)}`;
    delete requestData.body;
  }

  // parses response to JSON
  return fetch(url, requestData)
    .then(res => {
      return res.json();
    })
    .catch(err => {
      console.error(err);
    });
};