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Asynchronous JavaScript and XML – Part 2

Asynchronous JavaScript and XML – Part 2

AJAX – Server-side Approaches

A critical point in programming with AJAX is the need for client / server solutions but offline (offline in English) are beginning to see the day (running the client without the need to be connected to the Internet or a company intranet). AJAX does not need active code on the server (only the JavaScript code is running on the client), the latter being a Web server simply by sending web pages to the client. For languages such employees are interpreted and executed directly within the browser client. There is no need to deploy or upgrade a virtual machine (like Java for example) on the client. So AJAX is a portable solution, its various components according to W3C standards. Nevertheless, additional technologies may be used server-side, especially for data management in XML, such as scripting languages and databases (PHP and MySQL for example).

These choices are beyond the scope of AJAX, but can provide many additional services or information:

* Java provides a mature technology with support for lightweight processes (threads) and strong support of the Open Source community.
* PHP also has strong support from the Open Source community, including version 5 on more efficient management of XML natively.
* Perl has Catalyst particular.
* Python is a scripting language and full but less widely used than Java or PHP servers (Google uses it heavily).
* ColdFusion with bookstores CFjavax, Neuromancer, Sarissa, etc..
* Uniface 9.3 implements Ajax with Dynamic Pages

Competition for the display of dynamic content within a Web page is as follows:

* Flash and Flex (Adobe Systems)
* JavaFX (Sun Microsystems)
* Silverlight (Microsoft)
* Uniface (Compuware)
* XForms, the standard form proposed by the W3C.

AJAX – Advantages and disadvantages

The advantage of this method is primarily the speed at which an AJAX application responds to user actions, which are processed (partially at least) locally by the browser. Respecting largely Web standards (W3C and IETF), AJAX also has qualities of portability. Very quickly deployed, AJAX allows lower development costs of small applications and renewal costs of computer equipment, for AJAX works with relatively low hardware resources: simple client that does not require much memory (as opposed to technology JAVA), just a browser, a simple Web server. Only condition: choose a standards-compliant browser and also accepting the use of JavaScript (and in particular the XMLHttpRequest object), or adapt the code so that Web pages are read by any browser type (these browsers are increasingly rare) and the user does not wish to enable their functionality JavaScript enabled browser.

The user of AJAX applications is in effect authorized the execution of JavaScript code in its browser, which can raise fears about security issues (though there are antivirus blockers effective scripts). Not using the standard JavaScript XMLHTTP component, versions of Internet Explorer 5 or 6 for Windows must allow ActiveX, unlike other browsers (Firefox, Safari, Opera, etc.), But version 7 of IE is compatible . It is therefore advisable to test AJAX applications on each type of browser, due to non compliance by some Web browsers editors.

Another disadvantage is the issue of SEO because spiders are not able to index dynamically generated content.

By changing the context of navigation without the user not be alerted (by the way web access), AJAX poses many questions of accessibility. This is particularly true for users of screen readers or magnification devices (virtual magnifying glasses).

Finally, several cases of security vulnerabilities such as “code injection” were reported in 2005 and 2006 with AJAX solutions deployed in standard fashion. In this regard, we must remember that the majority of the applications deployed in a standard way are vulnerable. This recommendation is not specific to AJAX, it is valid for any technology and developments. As with almost any computer application, a security code, server and client is necessary with AJAX. This will result initially in a secure Web server and JavaScript code libraries, and, later client by updating the browser and install antivirus blocking malicious scripts.

As with any Web development, establish a connection through the secure https protocol is also a solution for secure exchanges between client and server distributing Web pages.



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