Parsing the returned JSON

Once the server returns the result, you need a way to get that result from the XMLHttpRequest object and convert the result from a string to a JavaScript object.

How to do it...

The XMLHttpRequest object defines the onreadystatechange attribute to which you assign a function that is called periodically throughout the lifespan of a request. Here's our doAjax function in its entirety, including a function assigned to this attribute to monitor the request for completion:

function doAjax() {
  var xmlhttp;
  xmlhttp = new XMLHttpRequest();

  var request = { 
    call: "kf6gpe-7"
  };

  xmlhttp.addEventListener("loadstart", loadstart, false);
  xmlhttp.addEventListener("progress", progress, false);  
  xmlhttp.addEventListener("load", load, false);
  xmlhttp.addEventListener("abort", abort, false);
  xmlhttp.addEventListener("error", error, false);

  xmlhttp.onreadystatechange = function() {
    if (xmlhttp...