Whats Ajax ?

AJAX stands for “Asynchronous JavaScript and XML”, but something tells me you already know that and want to know in layman’s terms.

Alright, AJAX is not a Programming Language nor it is a new Technology as many of us believes it to be. AJAX is nothing but a methodology based on Javascript,XML, xHTML and CSS.

Why AJAX ?

The main feature of AJAX is that it can post or get data from the server without reloading your page. Thats right, it makes a connection to the server using XML and get the required data as plain text or as XML.

Where to use ?

Its has various implementations in forms, validation, Interactive User interfaces etc etc. Thumbs rule is, you can use AJAX anywhere when you need to interact with server to fetch/post a small amount of data. An common example of AJAX implementation can be in the form where you want to check the availability of your desired username.

Any Limitations ?

As they say nothing is perfect, so it applies to AJAX too. It has following limitations:

1. As I am repeating again and again AJAX is only good to fetch and get small amount of data. So do not even think about posting a whole form via AJAX. That would defeat the whole purpose of AJAX.
2. AJAX can NOT post files as attachments or data to the server. Having said that there is a workaround to do that with the help of iframes.
3. As thy say, “..easy to use applications are difficult to code.” A simple page, which would have require a two page code, requires 3-4 files to work properly with AJAX.
4. AJAX is blamed to break the back button of the browser. Thats is why it is advisable to use AJAX only for small amount of data (see…I said that yet again )
5. AJAX will only work on new age browsers on Web and on Mobile, which has JavaScript enabled and support AJAX.

Final Word !
In the age of Web 2.0, where Web based application is looking in the eye of all existing desktop applications (including Microsoft Word), AJAX has become a necessary evil. It doesn’t matter if the application is a Desktop, Web or Mobile based, the bottom line is if you don’t implement AJAX in it…then its counterpart from Google will take the cake.

How to make an AJAX Call !

   1) Create and AJAX Object:

   function createAjaxObject() {

   //Code for Mozilla 
    if (window.XMLHttpRequest) { 
        return new XMLHttpRequest(); 
    } 
    //Code for IE 
    else if (window.ActiveXObject) { 
        return new ActiveXObject("Microsoft.XMLHTTP"); 
    } 
    else { 
        alert("Your browser does not support XMLHTTP."); 

    } 

} 
ajaxObj =  createAjaxObject();

2) Make a AJAX Call with or without parameters:
function makeAjaxCall() { 
    ajaxObj.onreadystatechange=handleAjaxResponse; 
    ajaxObj.open("get",url,true);
    ajaxObj.send(null);
}

3) Handle the response:
function  handleAjaxResponse() { 
    if (ajaxObj.readyState==0){
        //ajax is uninitialized 
    } 
    else if (ajaxObj.readyState==1){ 
        //ajax is loading 
    } 
    else if (ajaxObj.readyState==2){ 
        //ajax is loaded 
    } 
    else if (ajaxObj.readyState==3){ 
        //ajax is interactive 
    } 
    else if (ajaxObj.readyState==4){ 
        // get as Text 
        ajaxObj.responseText; 

        // or 

        // get as XML 
        ajaxObj.responseXML; 
    } 

}