21⟩ What is the W3C DOM?
The W3C Document Object Model (DOM) is defined by the W3C as the following: The Document Object Model is a platform- and language-neutral interface.
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28 Web Developers Questions And Answers
22⟩ What is XMLHttpRequest object in AJAX?
It offers a non-blocking way for JavaScript to communicate back to the web server to update only part of the web page.
23⟩ Which is the minimum version of PHP that needs to be running in order to use HTML_AJAX?
The oldest PHP version we've fully tested HTML_AJAX is 4.3.11, but it should run on 4.2.0 without any problems. (Testing reports from PHP versions older then 4.3.11 would be appreciated.)
24⟩ Explain the difference between proxied and proxyless calls in AJAX?
Proxied calls are made through stub objects that mimic your PHP classes on the JavaScript side in AJAX. E.g., the helloworld class from the Hello World example.
Proxyless calls are made using utility JavaScript functions like HTML_AJAX.replace() and HTML_AJAX.append() in AJAX.
25⟩ Which kinds of applications is best suited for Ajax?
We don't know yet. Because this is a relatively new approach, our understanding of where Ajax can best be applied is still in its infancy. Sometimes the traditional web application model is the most appropriate solution to a problem.
26⟩ Which parts of the HTML_AJAX API are stable?
We don't have a list right now, but most of the API is stable as of 0.3.0. There should be no major changes at this point, though there will be lots of new additions.
27⟩ Which JavaScript libraries and frameworks are available for AJAX support?
Prototype focuses on AJAX interactions including a JavaScript AJAX object that contains a few objects to do basic tasks such as make a request, update a portion of a document, insert content into a document, and update a portion of a document periodically. Prototype JavaScript library contains a set of JavaScript objects for representing AJAX requests and contains utility functions for accessing in page components and DOM manipulations. Script.aculo.us and Rico are built on top of Prototype and provide UI effects, support for drag and drop, and include common JavaScript centric widgets. If you are just looking to support AJAX interactions and a few basic tasks Prototype is great. If you are looking for UI effects Rico and Script.aculo.us are good options.
* Yahoo UI Library is a utility library and set of widgets using the APIs to support rich clients. The utility library includes support for cross-browser AJAX interactions, animation, DOM scripting support, drag and drop, and cross browser event support. The Yahoo UI Library is well documnented and contains many examples.
28⟩ Described applets and plugins?
Don't be too quick to dump your plugin or applet based portions of your application. While AJAX and DHTML can do drag and drop and other advanced user interfaces there still limitations especially when it comes to browser support. Plugins and applets have been around for a while and have been able to make AJAX like requests for years. Applets provide a great set of UI components and APIs that provide developers literally anything.
Many people disregard applets or plugins because there is a startup time to initialize the plugin and there is no guarantee that the needed version of a plugin of JVM is installed. Plugins and applets may not be as capable of manipulating the page DOM. If you are in a uniform environment or can depend on a specific JVM or plugin version being available (such as in a corporate environment) a plugin or applet solution is great.
One thing to consider is a mix of AJAX and applets or plugins. Flickr uses a combination of AJAX interactions/DHTML for labeling pictures and user interaction and a plugin for manipulating photos and photo sets to provide a great user experience. If you design your server-side components well they can talk to both types of clients.
