Ajax Programming :: The top 10 mistakes when using AJAX


	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 DHTML (DOM). 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 connections. 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 Mumbai Mobile:9892237486 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: - Hide quoted text - > 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 > DHTML (DOM). > 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 > connections. > 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 > Mumbai > Mobile:9892237486 > 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.