| By Mike Padilla |
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| December 5, 2007 10:30 AM EST |
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7,196 |
But interactions confined to a page level seemed somewhat stifling. So along came DHTML, the combination of HTML, CSS and JavaScript. Parts of the page could change instantaneously based on the user’s interaction without requiring a hit to the server. Information designers had a new tool to better manage screen real estate and interaction designers had a new tool for more discrete, sub-page level interactions. But DHTML interactions are fundamentally constrained. They can only manipulate information that is brought down to the client when the page initially loads. You can only bring down so much information at page load before the user gets frustrated with the initial load time.
Finally a subtle but powerful protocol was introduced by Microsoft - the XMLHttpRequest. It provided an API that can be used by JavaScript to establish asynchronous communication between the client and server. We were freed from the “new-information-from-server-requires-new-page load” constraint. By combining the power of webpage information manipulation of DHTML and the freedom of selectively exchanging relevant streams of data with the server in the background, the more rich and interactive user experiences of AJAX enhanced webpages were born.
Ultimately AJAX potentially affords improvements to the user experience by optimizing the two main factors in website performance – calls to the server and transmission of data to the client. As a result, AJAX can offer the following benefits and drawbacks:
Benefits
- A faster response. AJAX offers improved performance by retrieving a small bit of information and populating it into the existing context rather than having to retrieve an entirely new webpage just to view a small percentage of new content.
- A continuous, undisturbed user experience across a set of related, relevant interactions. The user’s context remains the same and the screen does not blink.
Drawbacks
- Loss of page state. Users mental model of the Web has been formed to expect page state behavior of browser back, forward, and bookmarking. AJAX breaks the page state.
- Loss of caching. When the user returns to a previously visited page, any AJAX content has to be reconstructed. This results in much slower response times due to the need to retrieve the content remotely rather than simply accessing it locally.
- Loss of search engine visibility.
- Accessibility issues.
While many AJAX toolkits are beginning to address these drawbacks, designers and developers need to assess whether the benefits of an AJAX enhanced user experience sufficiently outweighs the accompanying drawbacks.
Mike Padilla is a user experience manager at Vanguard. He has led front-end development efforts for such companies as Fleet Credit Cards, Mellon Private Asset Management, The Bank of New York, Radian Guaranty, and Bessemer Trust. Macromedia has featured his usability designs. He received a B.S. in mechanical engineering, focusing on ergonomics, from Cornell University.
Padilla is an ardent advocate of high-fidelity prototyping during requirements development. In his spare time, he designed and developed Protonotes, a free AJAX web service that allows project team members to discuss system functionality, design, and requirements directly on prototypes with "sticky notes".
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