// Create the request object
  var xml = new XMLHttpRequest();
  
  // Open the asynchronous POST request
  xml.open("GET", "/some/url.cgi", true);
  
  // We're going to wait for a request for 5 seconds, before giving up
  var timeoutLength = 5000;
  
  // Keep track of when the request has been succesfully completed
  var requestDone = false;
  
  // Initalize a callback which will fire 5 seconds from now, cancelling
  // the request (if it has not already occurred).
  setTimeout(function(){
      requestDone = true;
  }, timeoutLength);
  
  // Watch for when the state of the document gets updated
  xml.onreadystatechange = function(){
      // Wait until the data is fully loaded,
      // and make sure that the request hasn't already timed out
      if ( xml.readyState == 4 && !requestDone ) {
  
          // xml.responseXML contains the XML Document (if one was returned)
          // xml.responseText contains the response text (if no XML document was provided)
  
          // Clean up after ourselves, to avoid memory leaks
          xml = null;
      }
  };
  
  // Establish the connection to the server
  xml.send();