February 18, 2005
If anything about current interaction design can be called ¡°glamorous,¡± it¡¯s
creating Web applications. After all, when was the last time you heard someone
rave about the interaction design of a product that wasn¡¯t on the Web? (Okay,
besides the iPod.) All the cool, innovative new projects are online.
Despite this, Web interaction designers can¡¯t help but feel a little envious
of our colleagues who create desktop software. Desktop applications have a
richness and responsiveness that has seemed out of reach on the Web. The same
simplicity that enabled the Web¡¯s rapid proliferation also creates a gap between
the experiences we can provide and the experiences users can get from a desktop
application.
That gap is closing. Take a look at Google Suggest.
Watch the way the suggested terms update as you type, almost instantly. Now look
at Google Maps. Zoom in. Use your cursor
to grab the map and scroll around a bit. Again, everything happens almost
instantly, with no waiting for pages to reload.
Google Suggest and Google Maps are two examples of a new approach to web
applications that we at Adaptive Path have been calling Ajax. The name is
shorthand for Asynchronous JavaScript + XML, and it represents a fundamental
shift in what¡¯s possible on the Web.
Defining Ajax
Ajax isn¡¯t a technology. It¡¯s really several technologies, each flourishing
in its own right, coming together in powerful new ways. Ajax incorporates:
The classic web application model works like this: Most user actions in the
interface trigger an HTTP request back to a web server. The server does some
processing ¡ª retrieving data, crunching numbers, talking to various legacy
systems ¡ª and then returns an HTML page to the client. It¡¯s a model adapted from
the Web¡¯s original use as a hypertext medium, but as fans of The Elements of User Experience know,
what makes the Web good for hypertext doesn¡¯t necessarily make it good for
software applications.
Figure 1: The traditional model for web applications (left) compared to
the Ajax model (right).
This approach makes a lot of technical sense, but it doesn¡¯t make for a great
user experience. While the server is doing its thing, what¡¯s the user doing?
That¡¯s right, waiting. And at every step in a task, the user waits some
more.
Obviously, if we were designing the Web from scratch for applications, we
wouldn¡¯t make users wait around. Once an interface is loaded, why should the
user interaction come to a halt every time the application needs something from
the server? In fact, why should the user see the application go to the server at
all?
How Ajax is Different
An Ajax application eliminates the start-stop-start-stop nature of
interaction on the Web by introducing an intermediary ¡ª an Ajax engine ¡ª between
the user and the server. It seems like adding a layer to the application would
make it less responsive, but the opposite is true.
Instead of loading a webpage, at the start of the session, the browser loads
an Ajax engine ¡ª written in JavaScript and usually tucked away in a hidden
frame. This engine is responsible for both rendering the interface the user sees
and communicating with the server on the user¡¯s behalf. The Ajax engine allows
the user¡¯s interaction with the application to happen asynchronously ¡ª
independent of communication with the server. So the user is never staring at a
blank browser window and an hourglass icon, waiting around for the server to do
something.
Figure 2: The synchronous interaction pattern of a traditional web
application (top) compared with the asynchronous pattern of an Ajax application
(bottom).
Every user action that normally would generate an HTTP request takes the form
of a JavaScript call to the Ajax engine instead. Any response to a user action
that doesn¡¯t require a trip back to the server ¡ª such as simple data validation,
editing data in memory, and even some navigation ¡ª the engine handles on its
own. If the engine needs something from the server in order to respond ¡ª if it¡¯s
submitting data for processing, loading additional interface code, or retrieving
new data ¡ª the engine makes those requests asynchronously, usually using XML,
without stalling a user¡¯s interaction with the application.
Who¡¯s Using Ajax
Google is making a huge investment in developing the Ajax approach. All of
the major products Google has introduced over the last year ¡ª Orkut, Gmail, the latest beta version of Google Groups, Google Suggest, and
Google Maps ¡ª are Ajax applications. (For
more on the technical nuts and bolts of these Ajax implementations, check out
these excellent analyses of Gmail, Google
Suggest, and Google
Maps.) Others are following suit: many of the features that people love in
Flickr depend on Ajax, and Amazon¡¯s A9.com search engine applies similar
techniques.
These projects demonstrate that Ajax is not only technically sound, but also
practical for real-world applications. This isn¡¯t another technology that only
works in a laboratory. And Ajax applications can be any size, from the very
simple, single-function Google Suggest to the very complex and sophisticated
Google Maps.
At Adaptive Path, we¡¯ve been doing our own work with Ajax over the last
several months, and we¡¯re realizing we¡¯ve only scratched the surface of the rich
interaction and responsiveness that Ajax applications can provide. Ajax is an
important development for Web applications, and its importance is only going to
grow. And because there are so many developers out there who already know how to
use these technologies, we expect to see many more organizations following
Google¡¯s lead in reaping the competitive advantage Ajax provides.
Moving Forward
The biggest challenges in creating Ajax applications are not technical. The
core Ajax technologies are mature, stable, and well understood. Instead, the
challenges are for the designers of these applications: to forget what we think
we know about the limitations of the Web, and begin to imagine a wider, richer
range of possibilities.
It¡¯s going to be fun.
Ajax Q&A
March 13, 2005: Since we first published Jesse¡¯s essay,
we¡¯ve received an enormous amount of correspondence from readers with questions
about Ajax. In this Q&A, Jesse responds to some of the most common queries.
Q. Did Adaptive Path invent Ajax? Did Google? Did Adaptive
Path help build Google¡¯s Ajax applications?
A. Neither Adaptive Path nor Google invented Ajax. Google¡¯s
recent products are simply the highest-profile examples of Ajax applications.
Adaptive Path was not involved in the development of Google¡¯s Ajax applications,
but we have been doing Ajax work for some of our other clients.
Q. Is Adaptive Path selling Ajax components or trademarking
the name? Where can I download it?
A. Ajax isn¡¯t something you can download. It¡¯s an approach ¡ª
a way of thinking about the architecture of web applications using certain
technologies. Neither the Ajax name nor the approach are proprietary to Adaptive
Path.
Q. Is Ajax just another name for XMLHttpRequest?
A. No. XMLHttpRequest is only part of the Ajax equation.
XMLHttpRequest is the technical component that makes the asynchronous server
communication possible; Ajax is our name for the overall approach described in
the article, which relies not only on XMLHttpRequest, but on CSS, DOM, and other
technologies.
Q. Why did you feel the need to give this a name?
A. I needed something shorter than ¡°Asynchronous
JavaScript+CSS+DOM+XMLHttpRequest¡± to use when discussing this approach with
clients.
Q. Techniques for asynchronous server communication have
been around for years. What makes Ajax a ¡°new¡± approach?
A. What¡¯s new is the prominent use of these techniques in
real-world applications to change the fundamental interaction model of the Web.
Ajax is taking hold now because these technologies and the industry¡¯s
understanding of how to deploy them most effectively have taken time to develop.
Q. Is Ajax a technology platform or is it an architectural
style?
A. It¡¯s both. Ajax is a set of technologies being used
together in a particular way.
Q. What kinds of applications is Ajax best suited for?
A. 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.
Q. Does this mean Adaptive Path is anti-Flash?
A. Not at all. Macromedia is an Adaptive Path client, and
we¡¯ve long been supporters of Flash technology. As Ajax matures, we expect that
sometimes Ajax will be the better solution to a particular problem, and
sometimes Flash will be the better solution. We¡¯re also interested in exploring
ways the technologies can be mixed (as in the case of Flickr, which uses both).
Q. Does Ajax have significant accessibility or browser
compatibility limitations? Do Ajax applications break the back button? Is Ajax
compatible with REST? Are there security considerations with Ajax development?
Can Ajax applications be made to work for users who have JavaScript turned off?
A. The answer to all of these questions is ¡°maybe¡±. Many
developers are already working on ways to address these concerns. We think
there¡¯s more work to be done to determine all the limitations of Ajax, and we
expect the Ajax development community to uncover more issues like these along
the way.
Q. Some of the Google examples you cite don¡¯t use XML at
all. Do I have to use XML and/or XSLT in an Ajax application?
A. No. XML is the most fully-developed means of getting data
in and out of an Ajax client, but there¡¯s no reason you couldn¡¯t accomplish the
same effects using a technology like JavaScript Object Notation or any
similar means of structuring data for interchange.
Q. Are Ajax applications easier to develop than traditional
web applications?
A. Not necessarily. Ajax applications inevitably involve
running complex JavaScript code on the client. Making that complex code
efficient and bug-free is not a task to be taken lightly, and better development
tools and frameworks will be needed to help us meet that challenge.
Q. Do Ajax applications always deliver a better experience
than traditional web applications?
A. Not necessarily. Ajax gives interaction designers more
flexibility. However, the more power we have, the more caution we must use in
exercising it. We must be careful to use Ajax to enhance the user experience of
our applications, not degrade it.
Jesse James Garrett is the Director of User
Experience Strategy and a founder of Adaptive Path. He is the author of the
widely-referenced book The Elements of
User Experience.
Learn more about Ajax in our upcoming workshop, ¡°Designing and Building with
Ajax¡± on June 7, 2006 in Amsterdam, Netherlands.
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