PHP and MySQL Web Development 4th Ed-tqw-_darksiderg

Fundamental Ajax
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Note
For security reasons, the XMLHTTPRequest object can call URLs only within the same domain; it cannot
directly call a remote server.
The XMLHTTPRequest object is often referred to as the “guts” of any Ajax application
given that it is the gateway between the client request and the server response. Although
you will soon learn the basics of creating and using an instance of the XMLHTTPRequest
object, see http://www.w3.org/TR/XMLHttpRequest/ for a more detailed understanding.
The XMLHTTPRequest object has several attributes, as shown in Table 34.1.
Table 34.1 Attributes of the XMLHTTPRequest Object
Attribute
Description
onreadystatechange Specifies the function that should be invoked when the
readyState property changes.
readyState
The state of the of request, represented by integers 0 (uninitialized),
1 (loading), 2 (loaded), 3 (interactive), and 4 (completed).
responseText Contains data returned as a string of characters.
responseXml Contains data returned as an XML-formatted document object.
status An HTTP status code returned by the server, such as 200.
statusText
An HTTP status phrase returned by the server, such as OK.
The XMLHTTPRequest object has several methods, as shown in Table 34.2.
Table 34.2 Methods of the XMLHTTPRequest Object
Method
Description
abort()
Stops the request.
getAllResponseHeaders() Returns all the headers in the response as a string.
getResponseHeader(header) Returns the value of header header as a string.
open('method', 'URL', 'a') Specifies the HTTP method method (such as POST or
GET), the target URL URL, and whether the request
should be asynchronous (where a is ‘true’) or not (where a
is false).
send(content)
Sends the request, with optional POST content content.
setRequestHeader('x', 'y') Sets a parameter (x) and value (y) pair and sends it as a
header with the request.
Before using the functionality of XMLHTTPRequest, you must first create an instance of it.
This necessitates a bit more than simply typing
var request = new XMLHTTPRequest();