Understanding XMLHttpRequest
An object of XMLHttpRequest is used for asynchronous communication between client and server.
It performs following operations:
- Sends data from the client in the background
- Receives the data from the server
- Updates the webpage without reloading it.
Properties of XMLHttpRequest object
The common properties of XMLHttpRequest object are as follows:
| Property | Description |
|---|
| onReadyStateChange | It is called whenever readystate attribute changes. It must not be used with synchronous requests. |
| readyState | represents 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.
|
| reponseText | returns response as text. |
| responseXML | returns response as XML |
Methods of XMLHttpRequest object
The important methods of XMLHttpRequest object are as follows:
| Method | Description |
|---|
| 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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