Ajax Interview Question

1. What is Ajax?
-----------------
Asynchornized javascript and XML. It is used to retrive the data without refresh the page
or reloading page dynamically.

2. What type of status and readystate avaliable in Ajax?
--------------------------------------------------------

a. Ready state
0 - Request is not initilized
1 - Server connection establized (loading)
2 - Request Received (loaded)
3 - Processing Request (Interactive)
4 - Request Finished and response is ready (complete)

b. status
200 code - ok
404 code - page not found

3. XMLHttpRequest Object
----------------------------
It is used to exchange the data with server behind the page

New version Syntax
==================
xmlhttp=new XMLHttpRequest();

old version syntax
===================
xmlhttp=new ActiveXObject("Microsoft.XMLHTTP");

a. XMLHttpRequest object have two methods:

1. open(method,url,async)
method: the type of request: GET or POST
url: the location of the file on the server
async: true (asynchronous) or false (synchronous)

2.send(string)
Sends the request off to the server.
string: Only used for POST requests

b. XMLHttpRequest object Attribute

readyState the code successively changes value from 0 to 4 that means for "ready".

status 200 is OK

404 if the page is not found. responseText holds loaded data as a string of characters.

responseXml holds an XML loaded file, DOM's method allows to extract data. onreadystatechange property that takes a function as value that is invoked when the readystatechange event is dispatched.

4. Server Response

================

To get the response from a server, use the responseText or responseXML property of the XMLHttpRequst object.

a. responseText

document.getElementById("resultDiv").innerHTML=xmlhttp.responseText;

b. responseXML

xmlDoc=xmlhttp.responseXML;