ajax introduction

ajax
without loading the page u can send the data to server
and get from server
ajax means	asychronous javascript and xml
ajax just uses a browser built in object
xmlhttprequest
browser sent to server and get from server without page loading
when browser sent to server based on event mentioned
like browser loads
or page refreshs
keyup
mouse up
syntax for creating xml http request object
all browsers have built in object,
variable = new XMLHttpRequest();
older borwsers
variable = new ActiveXObject("Microsoft.XMLHTTP");
code to know it has this object or not
if (window.XMLHttpRequest) {
// code for modern browsers
xmlhttp = new XMLHttpRequest();
} else {
// code for old IE browsers
xmlhttp = new ActiveXObject("Microsoft.XMLHTTP");
}
objects or functions
new XMLHttpRequest()	Creates a new XMLHttpRequest object
abort()	Cancels the current request
getAllResponseHeaders()	Returns header information
getResponseHeader()	Returns specific header information
open(method, url, async, user, psw)	Specifies the request
	method: the request type GET or POST
	url: the file location
	async: true (asynchronous) or false (synchronous)
	user: optional user name
	psw: optional password
send()	Sends the request to the server
	Used for GET requests
send(string)	Sends the request to the server.
	Used for POST requests
setRequestHeader()	Adds a label/value pair to the header to be sent
function or object properties
onreadystatechange	Defines a function to be called when the readyState property changes
readyState	Holds the status of the XMLHttpRequest.
	0: request not initialized
	1: server connection established
	2: request received
	3: processing request
	4: request finished and response is ready
responseText	Returns the response data as a string
responseXML	Returns the response data as XML data
status	Returns the status-number of a request
	200: "OK"
	403: "Forbidden"
	404: "Not Found"
statusText	Returns the status-text (e.g. "OK" or "Not Found")