2. This is decidedly not a good idea for performance the way it’s described. If you need to make “multiple requests”, have all the necessary information at one point in time, but need to serialize them, then what you have is a single request. Otherwise, you’re just slowing everything down by creating unnecessary HTTP connections.

I stumbled on a library, called Flapjax, for reactive programming which makes this kind of pattern easy. The basic idea is that instead of using a callback model for coding reactive patterns, you chain functions on an event stream abstraction.

In this instance you would write something like this pseudo-code:
triggerEventStream.CallXHR(call1).CallXHR(call2).CallXHR(call3).
If you want to trigger it only once, you can have triggerEventStream be a stream with a single event.

I haven’t used that library yet, but the event stream abstraction seems really useful. It can also be used to handle reacting to UI events.

Here’s a good tutorial which explains how a naive Flapjax implementation might work: http://www.weaselhat.com/2007/08/11/lifting-in-flapjax/

seTimeout(function() {
var res1=$.ajax({url:”http://1″,async:false});
var res2=$.ajax({url:”http://2″,async:false});
var res3=$.ajax({url:”http://3″,async:false});

},0);

yeah, you’re the smart one out here. hopefully you’ve said enough and not find a need to say it again.

dwr.engine.beginBatch();
// Multiple Ajax calls go here
dwr.engine.endBatch();

You get the callbacks firing in the order you made the Ajax calls (which of course, thanks to DWR, look just like JavaScript function calls) and as an added bonus, you get only a single request made to the server (although it could be hitting multiple objects on the server).

I’ve said it before and I’ll say it again: if you’re doing Java-based Ajax work and not using DWR, up the dosage my friend :)