AJAX
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Its a web-technology, which speeds up web applications

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AJAX

Bharath. P Information Science dept.

Sapthagiri college of engineering


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Agenda

  • What is AJAX?

  • Overview

  • History

  • How it works?

  • Request phase implementation

  • Response phase implementation

  • Examples of Request and Response phase

  • Advantages and Disadvantages


What is ajax l.jpg
What is AJAX?

  • Asynchronous Javascript and XML.

  • It is a client-side technology that combines a set of known technologies in order to create faster and more user friendly web pages.

  • It provides responsiveness approaching to that of desktop applications.


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Overview

  • AJAX is meant to speed web apps that have frequent user interactions.

  • Technologies used mainly are javascirpt, xml, DOM, css…

  • It shortens the required time for both document transmission and document rendering.

  • When browser requests a new part of its displayed document from the server, it doesn’t lock up waiting for response, thus its Asynchronous.


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History

  • Use of <iframe> element which is made invisible by setting width and height to zero, although this worked, it was not elegant.

  • Microsoft introduced 2 extensions to DOM with XmlDocument and XmlHtml (XmlHttpRequest) objects.

  • It got popular from 2005/06 with google maps and gmail popularizing it.



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Request phase implementation

  • Object declaration of type XmlHttpRequest.

  • Registering function that implements the receive phase of the application using onreadystatechange property.

  • Call to open method to set parameters (Http method, URL of response document on the server, Asynchronous or synchronous) for HttpRequest.

  • Call to send method to send the HttpRequest to server.


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Response phase implementation

  • Check value of callback from server to see whether processing of request is completed.

  • Get the response using responsetext property of XmlHttprequest object.

  • Display the output in a desired way.


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Example of Request phase

  • Varxhr= new XmlHttpRequest();

    xhr.onreadystatechange= response;

    xhr.open(“GET”, “reply.php?....”,true);

    xhr.send(null);


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Example of Response phase

  • Function response()

    {

    if(xhr.readystate == 4) {

    var result=xhr.responsetext;

    // any desired code

    }


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Advantages

  • Independent of server technology.

  • Apart from obtaining the XMLHTTP object, all processing is same for all browser types, because Javascript is used.

  • Permits the development of faster and more interactive desktop like interface to users.


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Disadvantages

  • The back button problem. People think that when they press back button, they will return to the last change they made, but in AJAX this does not hold.

  • Requests ActiveX to be enabled in IE 5 and 6Is only available in newer versions of Opera, firefox and Safari

  • Has small implementation differences between browsers



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