a vanilla js ajax get request

ajaxRequest

function ajaxRequest(url, onSuccess, onError){
  var xmlhttp = new XMLHttpRequest(),
      response = null;
  xmlhttp.onreadystatechange = function() {
    if (xmlhttp.readyState == 4) {
      if(xmlhttp.status == 200){
        response = JSON.parse(xmlhttp.responseText);
        onSuccess(response);
      }
      else {
        onError(xmlhttp.responseText);
      }
    }
  };
  xmlhttp.open("GET", url, true);
  xmlhttp.send();
}