Why don't you use addEventListener for onlinestatechange?

 var xhr = new XMLHttpRequest();
xhr.open("GET", "/path/to/file", true);
xhr.onreadystatechange=function(){
  if(this.readyState===4&this.status===200){
    console.log(xhr.responseText);
  }
};
xhr.addEventListener('readystatechange', function(){
  if(this.readyState===4&this.status===200){
    console.log(xhr.responseText);
  }
});
xhr.send("");