AJAX Notes

AJAX

1.      AJAX= Asynchronous JavaScript and XML

2.      AJAX applications are Browser and platform independent

3.      XMLHttpRequest object: - is used to exchange data with a server behind the scenes. This means that it is possible to update parts of a web page without reloading the whole page.

4.      Syntax for creating XMLHttpRequest object:

Variable xmlhttp =new XMLHttpRequest ();      //for IE 7+, Firefox and chrome

Variable xmlhttp = new ActiveXObject (“Microsoft.XMLHTTP”);     //for IE 5 and IE 6

5.      To handle both type of browser:

Var xmlhttp;

If (window.XMLHTTPRequest)

{

// code for IE 7+, Firefox, chrome, opera, safari

            Xmlhttp= new XMLHTTPRequest ();

}

Else

{

            // code for IE 5 and IE 6

            Xmlhttp= new ActiveXObject (“Microsoft.XMLHTTP”);

}

6.      to send a request to a server, we use open() and send() methods of XMLHttpRequest object

xmlhttp.open (“GET”,”ajax.info.txt”,true);

xmlhttp.send ();

7.      Syntax is:

Open (method,URL,async)

Send (String)  //String is only used for post

8.      Two XMLHttpRequest object properties are:

a.      responseText

b.      responseXML

9.      the onereadystatechange event is triggered every time the ready state changes.

10.  Three important properties of the XMLHttpRequest object:

Property	Description
onreadystatechange	Stores a function (or the name of a function) to be called automatically each time the readyState property changes
readyState	Holds the status of the XMLHttpRequest. Changes from 0 to 4:  0: request not initialized  1: server connection established 2: request received  3: processing request  4: request finished and response is ready
status	200: "OK" 404: Page not found