AJAX wrapper for XMLHttpRequest supporting GET and POST

gistfile1.txt

/*
  data (optional) - a JSON string to send with the request
*/

function ajax(method, url, handler, data) {
  var xhr = new XMLHttpRequest();
  xhr.onreadystatechange = function(){
    if (this.readyState === 4) {
      if (this.status === 200) {
        handler(null, JSON.parse(this.responseText));
      } else {
        handler(this.statuscode, null);
      }
    }
  }
  xhr.open(method, url);
  if (method === 'POST') {
    xhr.setRequestHeader("Content-type", "application/json");
    xhr.setRequestHeader("Content-length", data.length);
    xhr.setRequestHeader("Connection", "close");
    xhr.send(data);
  } else {
    xhr.send();
  }
}

ajax('POST', 'https://secure-eyrie-78012.herokuapp.com/users', function(err, data){
  console.log(data);
}, JSON.stringify({firstName: "Kyle", lastName: "Coberly", role: 1}));