xmlHttpRequestExapmle.js

var xhr = new XMLHttpRequest();

xhr.open('GET', '/my/url'); //xhr.open(method, URL, async, user, password)

xhr.send(); //xhr.send([body])

//xhr.abort() to cancel the request

//also more convenience way to use
//onload onerror events
xhr.onreadystatechange = function() {
  /*
  const unsigned short UNSENT = 0; // initial state
  const unsigned short OPENED = 1; // open is triggered
  const unsigned short HEADERS_RECEIVED = 2; // receive headers
  const unsigned short LOADING = 3; // still is receiving packages
  const unsigned short DONE = 4; // request is done
  */
  if (this.readyState != 4) return;

  // after done, are available:
  // status, statusText
  // responseText, responseXML (when content-type: text/xml)

  if (this.status != 200) {
    // handle error
    alert( 'err: ' + (this.status ? this.statusText : 'something is wrong') );
    return;
  }

  // get result from this.responseText or this.responseXML
}