Order Prototype's Ajax.Request in a kind of Pipeline

[Kreisquadratur]

I'm in the situation, that a user could take actions which will
trigger several Ajax.Requests. The problem here is, that the browser
should stay responsive, so I need the asynchronous feature but the
responses from the server should not only have the same order as the
requests, but I also have to wait for the first answer before I can
send the second request. So like:

Request 1
Response to 1
Request 2
Response to 2
Request 3
Response to 3

Not:

Request 1
Request 2
Request 3
Response 1
Response 3
Response 2

And not even:

Request 1
Request 2
Request 3
Response 1
Response 2
Response 3

Why? Because the server responding me will lose/"forget" his current
answer, if another request comes in _and_ he can't even handle two
almost parallel requests.

I don't know how to change my code, cause functions like onSuccess
seem to run in a seperate "thread".

Anybody any idea?

 

[Tom de Neef]

I'm in the situation, that a user could take actions which will
trigger several Ajax.Requests. The problem here is, that the browser
should stay responsive, so I need the asynchronous feature but the
responses from the server should not only have the same order as the
requests, but I also have to wait for the first answer before I can
send the second request. So like:

Request 1
Response to 1
Request 2
Response to 2
Request 3
Response to 3

The XMLHttpRequest function has a onreadystatechange property which you can
use to test if it has completed successfuly (readyState=4). Put your
requests in an array and process the elements of this array in the event
handler. Somethin like:
// req assigned to the XMLHttpRequest object
var requests = [url1,url2,url3]
requests.reverse()
req.onreadystatechange = nextRequest

function nextRequest()
{ if ((req.readyState!=4) || (requests.length==0)) return
req.open("GET",requests.pop(),true)
}

Tom

 

[jdalton]

The Prototype user list is here (post your Prototype questions there):
http://groups.google.com/group/rubyonrails-spinoffs

A tutorial on Prototype and AJAX
http://www.prototypejs.org/learn/introduction-to-ajax

Ajax.Request is asynchronous by default which means you cannot
guarantee first-in-first out order.
You can however track the order via the onComplete or onSuccess
callbacks.
A simple example:
http://pastie.caboo.se/190523

- JDD