Building Applications Using Ajax

Building Applications using AJAX WebOSS ‘07 S Pradeep

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…

How AJAX is different

Need for AJAX To increase web's interactivity, speed and usability Issues with classic web applications * Almost all processing is done on server * High latency * 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 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 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 onreadystatechange 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 xhr.onreadystatechange=cbProcessResponse; xhr.open(’GET’,‘ajax.php’,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 // Our sample XML <?xml version=quot;1.0quot; encoding=quot;ISO-8859-1quot;?> <root> <response>OK</response> <msg>Hello World!</msg> </root> // 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 data are slightly simpler and slightly more in line with the rest of the JavaScript language than scripts for XML data. Find more about JSON at http://json.org //sample JSON { response: ‘OK’, msg: ‘Hello World’ }

JSON How? JSON can be generated by all the popular server-side languages. Native/Library Support // 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]) var pars = 'topic=ajax&framework=pjs'; Var url = '/cgi-bin/myAjaxHandler.cgi'; var myAjax = new Ajax.Request(url,{ method: quot;postquot;, // get/post parameters: pars, onComplete: cbProcessResponse // Our old callback function }); Ajax.PeriodicalUpdater(container, url[, options])

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 AJAXIAN - http://ajaxian.com AJAX info - http://ajaxinfo.com AJAX Lesson - http://ajaxlessons.com Go4Expert - http://go4expert.com

Thanks! Hussain Fakhruddin Teknowledge Software The wonderful audience.

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Building Applications Using Ajax

by s_pradeep on Oct 14, 2007

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