xhr_promise.js

function get(url) {
  return new Promise(function(resolve, reject) {
    var xhr = new XMLHttpRequest();
    xhr.open('GET', url);
    
    xhr.onload = function() {
      if (xhr.status === 200) {
        resolve(xhr.response);
      } else {
        reject(Error(xhr.statusText));
      }
    };
    xhr.onerror = function() {
      reject(Error('Something not expected happened. Please check network connection'));
    };
    xhr.send();
  });
}