Sequence of steps executed in Ajax call

Hi All,

I'm very new to Ajax and started with a tutorial given at http://www.ibm.com/developerworks/library/j-ajax1/. . But instead of working on Shopping cart example, I replaced that with a TimeServlet that returns the current time. Servlet is working fine and I'm pasting any details about it here.

But below are my ajax calls

function newXmlHttpRequest(){
              // obtain a XMLHttpRequest object 
       }

function getReadyStateHandler(ajxReq, ajxResHandler) {

// Return an anonymous function that listens to the 
	    // XMLHttpRequest instance
	    return function () {
		  alert("Request state "+ajxReq.readyState);
	         if (ajxReq.readyState == 4) {
	    	
	    	    if (ajxReq.status == 200) {
		    	  ajxResHandler(ajxReq.responseText);
		      } else {
		        alert("HTTP error: "+req.status);
		      }
	        }
	    };
     }

function getTime() {
	
	   var req = newXmlHttpRequest();

// Set the handler function to receive callback notifications
          // from the request object
          req.onreadystatechange = getReadyStateHandler(req, resHandler);
          req.open("GET", "http://localhost:8080/sampleajax/timeservlet/", true);

// Specify that the body of the request contains form data
          req.setRequestHeader("Content-Type","text/html");
          req.send(null);
   }

function resHandler(response){
	document.getElementById("time").innerHTML = response;
  }

I'm calling getTime() function on onload event of the webpage. I'm getting response properly as expected. To trace the call, I used alert statement displaying the request.readyState and what I noticed in getReadyStateHandler() function, it get started with readyState as 1 and does not go in sequence like 1, 2, 3, 4 , instead I see 1, 2, 4 and 3.. and some times 1,2,3, 4,4 .. Is there any error in the way I'm making the ajax calls. Or I don't have to worry about the calls. Please advise.

Using alert for debugging can lead to some weird timing issues.

You really should use console.log() and log to the JavaScript console. With Firefox, you can use Firebug. Chrome and IE8+ have the console built in.

Eric

Hmm, Thanks Eric. I will try console logging instead of Alerts.

As a side note to this question, I was also browsing Log4Javascript library. Is that worth using ?

I have not used it.

Eric

I'd try using the built-in logging first and bring in bigger guns only if necessary.