Consider the following AJAX code:

function loadReport() {
  var xhttp = new XMLHttpRequest();
  xhttp.onreadystatechange = function() {
    if (this.readyState == 4 && this.status == 200) {
    document.getElementById("data").innerHTML = this.responseText;
    }
  };
  xhttp.open("GET", "report.txt", true);
  xhttp.send();
}

The readyState property holds the status of the XMLHttpRequest. So, this.readyState == 4 means that