XMLHttpRequest (XHR): It is used for asynchronous communication between client and server and send HTTP or HTTPS requests to a web server and load the server response data back into the script.
It performs following operations:
Create an XMLHttpRequest Object
var xmlHttpRqst = new XMLHttpRequest(); For All modern browsers (Chrome, Firefox, IE7+, Edge, Safari, Opera) var xmlHttpRqst = new ActiveXObject("Microsoft.XMLHTTP"); For IE5 and IE6| 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, password) | method: the request type GET or POST url: the file location async: true (asynchronous) or false (synchronous) user: optional user name password: optional password |
| send() | Sends the GET request. |
| send(string) | Sends the POST request. |
| setRequestHeader() | It adds request headers. |
Properties of XMLHttpRequest object are as follows:
| 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 : request not initialized 1 : server connection established 2 : request received 3 : processing request 4 : request finished and response is ready |
| reponseText | returns response as text. |
| responseXML | returns response as XML. |
| 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") |