AJAXs (Asynchronous JavaScript And Xmls)
a competitor to Applets. AJAX (Asynchronous JavaScript And Xml)
is not a language or a software package or even an interface. It’s a word
someone invented for the generic concept of having JavaScript talk directly to the
server without reloading the HTML (Hypertext Markup Language) page. There
are any number of possible ways of implementing AJAX.
The most common is to use the non-standard XmlHttpRequest class, which is available from JavaScript in most major
browsers.
The major defining characteristic, though, is the asynchronous aspect of the
technology. Even XML (extensible Markup Language) is in there by coincidence; people describe things as
AJAX applications when they don’t use
XML
at all. There is no new language or file format here. There’s no specification;
no definition of what AJAX
is or is not. There are no special tools. There’s no visual appearance that
could be created except what you could do with a web browser,
HTML,
JavaScript and CSS (Cascading Style Sheets) anyway. In fact, if you were allowed to stub out the
data, you could write any AJAX application with only those basic client-side web
technologies.
AJAX
is typically a generic JavaScript program to allow thin clients to do field
validation (by asking the server) without refreshing the entire page. Google uses it
for maps. It works by sending standard HTTP (Hypertext Transfer Protocol)
queries to the server. Your application specific code all lives on the server.
AJAX
has the following advantages over Applets:
- JavaScript generally starts faster than an Applet.
The browser preloads the JavaScript run time, but delays loading the Applet JVM (Java Virtual Machine)
until first use. The load overhead for JavaScript gets buried in the browser
start up time, when the JVM load gets blamed on the first Applet. The JVM
is a much bigger and more complex animal than the JavaScript runtime.
- AJAX is really just HTML
and JavaScript and CSS, so it acts like a web browser. That is,
you can resize the window and expect to see text and tables wrapped and presented
in all the normal ways. All the UI (User Interface)
kludginess of Applets is gone.
- JavaScript comes pre-installed where Java does not.
- Both Applets and AJAX allow user interaction without the delay of a round
trip to the server.
AJAX
has the following disadvantages:
- Java is object oriented. It won’t fall apart under its own weight as
project complexity grows as JavaScript apps will.
- JavaScript has many bugs and platform-specific eccentricities. A properly
written AJAX
application should have a pure-HTML fallback in case the JavaScript does not
work.
- JavaScript might be looked on as a limited or toy language designed for
scripting inside a browser. Java is a general purpose language suited for pretty
well any sort of computation.
- Java security is tighter. Unsigned Applets are less potentially dangerous.
Sooner or later after a major scare, corporate America is going to ban JavaScript
from their machines because of security risks. At that point, all legitimate
AJAX
code will stop working, so I consider it irresponsible to go the
AJAX
route.
- JavaScript is not properly supported on mobile devices.
- JavaScript does not work for the visually impaired.
- Firefox has a popular plug-in NoScript which blocks
Javascript. Not everyone uses it but a lot of security conscious folks do use
it.
- There are 2 to 4 browser
exploits and security holes a month and about 80% of the
time the advice is until the manufacturer has a patch
finished, the problem can be avoided by disabling JavaScript.
Microsoft has embraced AJAX and renamed it Atlas, which presumably means they are busy figuring
out how to lock AJAX apps into Microsoft and make sure Java apps stop
running.
Books
Book referral for Pragmatic Ajax, A Web 2.0 Primer
 |
recommend book⇒Pragmatic Ajax, A Web 2.0 Primer |
| by |
Pragmatic Bookshelf |
978-0-9766940-8-3 |
paperback |
|---|
| publisher |
Pragmatic Bookshelf |
|---|
| published |
2006-04-10 |
|---|
| Covers Ajax with Java, .NET and Ruby on Rails server frameworks. |
|
| Greyed out stores probably do not have the item in stock. Try looking for it with a bookfinder. |
