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Step by Step to AJAX


AJAX has been exciting many programmers as the latest and greatest thing in web development. This article takes a step-by-step look at the Microsoft way to script for AJAX.

Author Info:
By: Jayaram Krishnaswamy
Rating: 4 stars4 stars4 stars4 stars4 stars / 114
November 30, 2005
TABLE OF CONTENTS:
  1. · Step by Step to AJAX
  2. · Ajax's Model of Interaction
  3. · XmlHttpRequest
  4. · XMLHttpRequest Object Methods
  5. · Fetching a page using AJAX

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Step by Step to AJAX - XMLHttpRequest Object Methods
(Page 4 of 5 )

This short list of methods is shared by all supported browsers. In this tutorial we shall look at some of the highlighted methods.

abort()
current request is stopped
getAllResponseHeaders()
returns a string containing information of headers
getResponseHeader ("headerlabel")
returns a string containing information about a single header
open("method", "URL"[,asyncFlag[,"userName"[,"password"]]])
assigns various request attributes
send(content)
Transmits the data with information that may be posted, if needed
setRequestHeader ("label", "value")
assigns label, value pair for the header

While open() and send() are most often used, the others are also useful in some cases. The open() method begins the interaction and takes two mandatory arguments; the "method" used to open, which is either GET or POST, and the URL to which the request is made.

The GET and POST methods are similar to those used in ASP, as some of you might recognize. The GET is indicated for retrieving read only data while POST is for sending data to the server.

The URL could be complete, or a relative URL.

The third parameter which is optional (default value TRUE being asynchronous) sets the interaction to be synchronous (FALSE) or asynchronous (TRUE). If you choose the synchronous route, the script waits for the response to arrive before acting. The useful mode is to set the interaction to be asynchronous and use the  onreadystatechange event (to be discussed) to get at the response.

XMLHttpRequest Object Properties

The following read only properties are browser agnostic (all supported browsers understand them).

onreadystatechange
Event handler which fires every time the state changes
readState
Integer representing the status of the object
0 = uninitialized
1 = loading
2 = loaded
3 = interactive
4 = complete
responseText
Data returned in string format
responseXML
Data returned in DOM Compatible format
status
Numeric code returned by server indicating status
404: Not found
200: OK
statusText
Message string that came with the status


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