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Thursday, 25 September 2014

ajax tutorial for beginners

Send a Request To a Server

To send a request to a server, we use the open() and send() methods of the XMLHttpRequest object:"GET","ajax_info.txt",true);

Method Description
open(method,url,async) Specifies the type of request, the URL, and if the request should be handled asynchronously or not.

method: the type of request: GET or POST
url: the location of the file on the server
async: true (asynchronous) or false (synchronous)
send(string) Sends the request off to the server.

string: Only used for POST requests


GET is simpler and faster than POST, and can be used in most cases.
However, always use POST requests when:
  • A cached file is not an option (update a file or database on the server)
  • Sending a large amount of data to the server (POST has no size limitations)
  • Sending user input (which can contain unknown characters), POST is more robust and secure than GET

Server Response

To get the response from a server, use the responseText or responseXML property of the XMLHttpRequest object.
Property Description
responseText get the response data as a string
responseXML get the response data as XML data

The responseText Property

If the response from the server is not XML, use the responseText property.
The responseText property returns the response as a string, and you can use it accordingly:



The onreadystatechange event

When a request to a server is sent, we want to perform some actions based on the response.
The onreadystatechange event is triggered every time the readyState changes.
The readyState property holds the status of the XMLHttpRequest.
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
In the onreadystatechange event, we specify what will happen when the server response is ready to be processed.
When readyState is 4 and status is 200, the response is ready:


  if (xmlhttp.readyState==4 && xmlhttp.status==200)

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