*~my Fetch~*

myfetch.js

const fetch = (url, verb, onSuccess, onFail) => {
  const asyncqued = !!onSuccess;
  asyncqued && req.onreadystatechange = processReqChange;

  const req = (window.XMLHttpRequest && new XMLHttpRequest()) 
    || (window.ActiveXObject && new ActiveXObject("Microsoft.XMLHTTP"));

  callback(req, onSuccess, onFail);

  req.open(verb, url, asyncqued);
  req.send(null);

  return asyncqued ? req : req.responseText;
} 

const callback = (req, onSuccess, onFail) => {
  if (req.readyState == 4) {
    if (req.status == 200) {
      onSuccess && onSuccess(req.responseText, url, req); 
    } else {
      onFail && onFail(url, req);
    }
  }
}