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The top 10 mistakes when using AJAX

  The top 10 mistakes when using AJAX

The last months I found more and more web sites that make a heavy use of
AJAX to be on the Web 2.0 train, but a lot of them are very strange because
they are slower than before, you will get more errors and sometimes nothing
does work ( i.e. when running on a mobile device). Here are my top 10
mistakes when using AJAX (not depending which framework you want to use):

1.      Don't use AJAX to update the complete page by putting everything in
a UpdatePanel. You want to save time and traffic when running the web page.
Never update parts of the web site that can be changed using JavaScript and

2.      Have in mind that there are a couple of visitors that have
JavaScript disabled or using a web browser with an older or less JavaScript
implementation like the most mobile devices have. What does your visitor see
if everything is disabled? I don't recommend to have the full web site
available as a JavaScript disabled version!

3.      Cache the same requests on client-side web browser or implement any
caching on the web server. The most used scenarios like AutoComplete or
DropDown fields are filled everytime the same. A wrong written AutoComplete
can slow down your web server (database server) because there more requests
done than the version before using PostBacks. Think of pressing F5 (reload)
all the time with your old web site. If you have cascading DropDown you can
save more traffic/requests!

4.      Don't run concurrent or long running AJAX requests when using CSS or
JavaScript to change the UI. There are only two concurrent http connections
possible with all common web browsers (I know you can change this, but the
default behavior is set to two). If there are running to many AJAX requests
running loading of images will be slow down.

5.      Use everytime the asynchrouns invoke of the send method of
XMLHttpRequest. There is no issue where you want to use the synchronous one.
Your web browser will not be forozen when having network problems or slow

6.      Try your web application using a very slow internet connection. Try
it again using a TCP/IP connection with a very high latency for each paket.

7.      Is your web application running as a desktop replacement? Have a
look at the memory usage of common web browsers if you run your application
one hour, two hours or couple of days. Not everybody has a development
machine like yours!

8.      Check the http status code you will get back from XMLHttpRequest.
There are a couple of common network errors like DNS not available, http
server error 500. Did you ever checked for the status code which tells you
if your web browser is in offline mode?

9.      Try to disable the XMLHttpRequest object! With IE7 you can use the
native object instead of the ActiveX object, but you can still disable the
native object, too.

10.  Check your AJAX requests for security issues! Did you simple open all
your data access layers? Make use of FormsAuthentication and
PrincipalPermissions on ASP.NET. Can anybody create requests (not only by
clicking on a link)?

I know there are more issues where we should have a eye on. My experience is
that there is a high need for deciding where and when to use AJAX.

Thanks and Regards

Rajagopal G
Chrysalis Information Systems

you also must write the www in the url , for ajax , if you load a page
without the www in the url an error msg will pop!

On Nov 22, 8:46 am, "Raja Gopal" <gandhe.swa@gmail.com> wrote:

> you also must write the www in the url , for ajax , if you load a page
> without the www in the url an error msg will pop!

That is to say, I guess, that it doesn't automatically add the 'www.'
if the non-www URL doesn't work (like a browser's address bar most
probably will). However, some servers are set up so that they work
equally well with and without the 'www.' part, and thus should continue
to work normally. But that is only my speculation, and not actual
research I've done.
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