Building Applications using AJAX

pradeep's Avatar author of Building Applications using AJAX
This is an article on Building Applications using AJAX in JavaScript and AJAX.
The first of its kind Web Technology Conference on Open Source Technology, WebOSS '07 was organised in Kolkata on Sat, 13th Oct 07 and I spoke at the event as one of the participants on "Building Applications using AJAX". Here I will share my presentation, the PDF copy download requires you to register at the forum.

What is AJAX?

  • AJAX = Asynchronous JavaScript And XML
  • Is a web development technique used for creating faster, interactive web applications.

Who uses AJAX?


  • Google maps
  • Gmail
  • Google Suggest
  • Flickr
  • del.icio.us
  • Meebo
  • and many more websites…

How AJAX is different





Need for AJAX


  • To increase web's interactivity, speed and usability
  • Issues with classic web applications
  1. Almost all processing is done on server
  2. High latency
  3. Low interactivity

Benefits of Using AJAX


  • Enhance your sites by allowing quicker access to data.
  • Reduce the amount of bandwidth used in data presentation.
  • Make a web application that feels more like a native application.

AJAX Workarounds


  • Hidden IFRAME
  • <SCRIPT> src hack
  • Cookies

Where to use AJAX


  • Anywhere you have a search box, adding Google suggest functionality.
  • Pages where you have a multi-step process.
  • When working with large or highly interdependent datasets.

Simple Ajax Application : How To


  • Create a request object
  • Make the request
  • Handle the response

Create a request object



Code:
if browser is mozilla or safari or opera then
 	create a new XMLHttpRequest
 otherwise if browser is IE
 	create a new ActiveXObject
 otherwise
 	error - browser does not support XMLHttpRequest
  • IE 5,5.5,6 implement XHR as an ActiveX object (Msxml2.XMLHTTP/Microsoft.XMLHTTP)
  • Mozilla 1.0+, Safari 1.2+, Opera 8+, IE7 provide XMLHttpRequest natively.
  • All XHR objects have the same methods and properties.
Code

Code: JavaScript
var xhr = null;
 if(window.XMLHttpRequest) // Mozilla,Safari, etc.
 {
     xhr = new XMLHttpRequest();
 }
 else if(window.ActiveXObject) // < IE 7
 {
     xhr = new ActiveXObject('Microsoft.XMLHTTP');
 }
 else
 {
     alert('Oops! Your browser does not support XMLHttpRequest');
 }

XHR Methods


  • open('method','url',asyncFlag)
  • send(content)
  • abort()
  • getResponseHeader("header")
  • setRequestHeader("header","value")

XHR properties


  • onreadstatechange
  • readystate
  • responseText
  • responseXML
  • status
  • statusText

Make the request


  • set onreadystatechange to callback function cbProcessResponse
  • open a request on the XHR object
  • send the request through the XHR object
  • "Same Site" rule
  • "GET" or "POST"
  • Asynchronous flag
Code

Code: JavaScript
xhr.onreadystatechange=cbProcessResponse;
 xhr.open('ajax.php','GET',true);
 
 function cbProcessResponse()
 {
     if(xhr.readystate==4 && xhr.status==200)
     {
         alert(xhr.responseText);
     }
 }
 
 /* readystate values
 0 -> uninitialized
 1 -> loading
 2 -> loaded
 3 -> interactive
 4 -> completed
 */

Handle Response: Parsing the XML



Code: XML
// Our sample XML
 <?xml version="1.0" encoding="ISO-8859-1"?>
 <root>
     <response>OK</response>
     <msg>Hello World!</msg>
 </root>
Code: JavaScript
// Revised callback function
 function cbProcessResponse()
 {
     if(xhr.readystate==4 && xhr.status==200)
     {
       var xmlDoc = xhr.responseXML.documentElement;
       var s = x.getElementsByTagName('response')[0].firstChild.data;
       var m = x.getElementsByTagName('msg')[0].firstChild.data;
       alert('Response Code:'+s+'\nMessage: '+m)
     }
 }

Enter JSON


  • JavaScript Object Notation
  • JSON is a lightweight data-interchange format.
  • JSON is easier to parse and has less overhead when compared to XML.
  • Find more about JSON at http://json.org
Code: JavaScript
//sample JSON
 {
     response: 'OK',
     msg: 'Hello World'
 }

JSON How?


  • JSON can be generated by all the popular server-side languages.
  • Native/Library Support
Code: JavaScript
// Revised callback function to use JSON
 function cbProcessResponse()
 {
     if(xhr.readystate==4 && xhr.status==200)
     {
       var jsonData = eval('('+xhr.responseText+')');
       var s = jsonData.response; // easy ;-)
       var m = jsonData.msg;
       alert('Response Code:'+s+'\nMessage: '+m)
     }
 }
Doesn't that look simpler?

Frameworks


  • A framework is a re-usable design for a software system with built-in generic functions for performing repetitive, natively unsupported operations.
  • The Prototype JavaScript Framework is a JavaScript framework that provides an Ajax framework and other utilities.
  • Download from http://prototypejs.org
  • Others: YUI, Dojo, jQuery, mooTools

Using Prototype.js


  • Prototype provides the Ajax object to abstract the different browsers.
  • Ajax.Request()
  • Ajax.Updater(container, url[, options])
  • Ajax.PeriodicalUpdater(container, url[, options])
Code: JavaScript
var pars = 'topic=ajax&framework=pjs';
 Var url = '/cgi-bin/myAjaxHandler.cgi';
 var myAjax = new Ajax.Request(url,{
         method: "post", // get/post
         parameters: pars,
         onComplete: cbProcessResponse // Our old callback function
          });

AJAX Security


  • Data Validation
  • Authentication
  • Test your code thoroughly before deployment.

Tips


  • Don't overuse AJAX, the usability requirements for JavaScript applications are quite different than the requirements for regular web pages.
  • Escape content sent to the server.
  • Use AJAX activity indicators.
  • http://www.napyfab.com/ajax-indicators/

Debugging AJAX


  • Always test your PHP/Server-side code before integrating it with the JavaScript side.
  • Always check xhr.status
  • Use FireBug to pin-point errors, and trace performance bottle-necks.
  • Download from http://www.getfirebug.com/

Resources


Download The Presentation



http://www.slideshare.net/s_pradeep/...ons-using-ajax
Izaan's Avatar, Join Date: Oct 2007
Skilled contributor
Nice one.
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