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Ajax: A New Approach to Web Applications
by Jesse James Garrett
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:
standards-based presentation using XHTML and CSS;
dynamic display and interaction using the Document Object Model;
data interchange and manipulation using XML and XSLT;
asynchronous data retrieval using XMLHttpRequest;
and JavaScript binding everything together.
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 — retrieving data, crunching numbers, talking to various legacy systems — 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.
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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 — an Ajax
engine — 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 — 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 — 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.
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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 — such as simple data validation, editing data in memory, and
even some navigation — the engine handles on its own. If the engine needs something from the server in order to respond — if it’s
submitting data for processing, loading additional interface code, or retrieving new data — 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 —
Orkut, Gmail, the latest beta version of Google Groups, Google Suggest, and Google Maps — 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
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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 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?
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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 President and a founder of Adaptive Path. He is the author of the widely-referenced book The Elements of
User Experience. Jesse’s other essays include The Nine Pillars of Successful Web Teams and Six Design Lessons From the Apple
Store.
To get essays like this one delivered directly to your inbox, subscribe to our email newsletter. For more, check out our blog.
This work is licensed under a Creative Commons License.
Published by Adaptive Path | 363 Brannan St. | San Francisco, CA 94107 | 1-415-495-8270 | http://adaptivepath.com/
