fetchXHR.js

function fetchXHR (url, httpMethod, body) { // httpMethod is optional
  var xhr = new XMLHttpRequest();
  var promise = new Promise(function (resolve, reject) {
    xhr.onreadystatechange = function () {
      if (xhr.readyState !== 4) return
      if (xhr.status >= 200 && xhr.status < 300) resolve(xhr.response)
      else reject({status: xhr.status, statusText: xhr.statusText, xhr:xhr})
    }
    xhr.open(httpMethod || 'GET', url, true)
    xhr.send(body)
  })
  promise.abort = function() { xhr.abort() }
  promise.xhr = xhr
  return promise
}