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Understanding XMLHttpRequest

An object of XMLHttpRequest is used for asynchronous communication between client and server.

It performs following operations:

  1. Sends data from the client in the background
  2. Receives the data from the server
  3. Updates the webpage without reloading it.

Properties of XMLHttpRequest object

The common properties of XMLHttpRequest object are as follows:

onReadyStateChangeIt is called whenever readystate attribute changes. It must not be used with synchronous requests.
readyStaterepresents the state of the request. It ranges from 0 to 4.

0 UNOPENED open() is not called.

1 OPENED open is called but send() is not called.

2 HEADERS_RECEIVED send() is called, and headers and status are available.

3 LOADING Downloading data; responseText holds the data.

4 DONE The operation is completed fully.

reponseTextreturns response as text.
responseXMLreturns response as XML

Methods of XMLHttpRequest object

The important methods of XMLHttpRequest object are as follows:

void open(method, URL)opens the request specifying get or post method and url.
void open(method, URL, async)same as above but specifies asynchronous or not.
void open(method, URL, async, username, password)same as above but specifies username and password.
void send()sends get request.
void send(string)send post request.
setRequestHeader(header,value)it adds request headers.
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