Vanilla Javascript AJAX Function

ajax_request.js

var http_request = new XMLHttpRequest();
http_request.open("GET", "{% url 'api_categories' %}");
http_request.send(null);
http_request.onreadystatechange = function(){
  var DONE = 4;
  var OK = 200;
  if (http_request.readyState === DONE){
    if (http_request.status === OK){
      console.log(http_request.responseText);
    } else {
      console.log("Error: " + http_request.status);
    }
  }
}