The XMLHttpRequest Object
XMLHttpRequest is an API that facilitates to and fro exchange of data between a client and a server. Here we explore the most commonly used properties and methods of the
onreadystatechange property has an event handler which is called everytime the
readystatechange event is fired, which in turn is fired every time the
readyState attribute of the
XMLHttpRequest object changes.
readyState attribute gives the state of the
XMLHttpRequest client in integer values from 0 to 4. 0 - uninitialized. 1 -
open() method called successfully; connection with server established. 2 -
send() method called; HTTP response headers have been received. 3 - data is being received;
responseText property holds partial data. 4 - request operation for transfer of data from the server is completed.
status property returns standard HTTP status codes. For example,
status value of 200 denotes "Ok" and 404 "Not Found".
responseText returns the response data as a string.
responseXML returns the response data as XML.
open() method initializes HTTP/HTTPS requests of the
XMLHttpRequest object and can accept upto five parameters.
open(method, url, async, user, password);
method parameter can have
HEAD values. The
url parameter is the URL to send the request to, either absolute or relative. The
async parameter takes a Boolean value:
true for asynchronous requests and
false for synchronous requests. The
user parameter is the name of the user for authentication, but is optional. By default, it is an empty string. The
password parameter is another optional parameter for authentication which, by default, is also an empty string.
send() method sends the request to the server. For
GET method, there is no parameter required. But to send data with the request using the
POST method, a single parameter containing the data has to be passed to
send(), for example,