AJAX And Usability Issues
AJAX and Usability
Although, as described in [1] AJAX can enhance the usability of Web-based services developers need to be aware of various usability problems which may be encountered.
Challenges For AJAX Developers
Concept of State
Once a Web page has been downloaded it has traditionally remained static. AJAX uses dynamic Web page updates which means that state transition (the move from one page view to another) is more complex, as separate elements may update asynchronously. AJAX applications frequently do not store application state information; this breaks the 'back' button functionality of the browser. Many Web users use the back button as their primary means of navigation and struggle to control the system without it.
AJAX requires developers to explicitly support this functionality in their software, or use a framework that supports it natively. Various solutions to this problem have been proposed or implemented, such as the use of invisible IFRAME elements that invoke changes which populate the history originally used by the browser's back button.
A related issue is that as AJAX allows asynchronous data exchange with the server, it is difficult for users to bookmark a particular state of the application. Solutions to this problem are appearing. Some developers use the URL anchor or fragment identifier to keep track of state and therefore allow users to return to the application in a given state.
The asynchronous nature of AJAX can also confound search engines which traditionally record only a page's static content. Since these usually disregard JavaScript entirely, an alternative access must be provided if it is desirable for a Web page to be indexed.
User Expectations
There are certain expectations of how Web-based information will be displayed and processed. Without explicit visual clues to the contrary, users are unlikely to realise that the content of a page is being modified dynamically. AJAX applications often do not offer visual clues if, for example, a change is being made to the page or content is being preloaded. The usual clues (such as the loading icon) are not always available. Solving this requires designers to explicitly support this functionality, using traditional user interface conventions wherever possible or alternative clues where necessary.
Response Time
AJAX has the potential to reduce traffic between the browser and the server as information can be sent or requested as and when required. However, this ability can easily be misused, such as by polling the server for updates excessively frequently. Since data transfer is asynchronous, a lack of bandwidth need not be perceivable to the user; however, ensuring this is the case requires smart preloading of data.
Design Issues
AJAX provides techniques that previously were available only by using DHTML or a technology like Flash. There is a concern that, as with previous technologies, designers have access to a plethora of techniques that bring unfamiliar usability or accessibility problems. Gratuitous animation, pop ups, blinking text and other distractions all have accessibility implications and stop the user from fully focussing on the task at hand.
Accessibility
Most methods of AJAX implementation rely heavily on features only present in desktop graphical browsers and not in text-only readers. Developers using AJAX technologies in Web applications will find attempting to adhere to WAI accessibility guidelines a challenge. They will need to make sure that alternate options for users on other platforms, or with older browsers and slow Internet connections, are available.
Conclusions
The concerns surrounding adoption of AJAX are not unfamiliar. Like Flash, the technologies comprising AJAX may be used in many different ways; some are more prone to usability or accessibility issues than others. The establishment of standard frameworks, and the increasing standardisation of the technologies behind AJAX, is likely to improve the situation for the Web developer.
In the meantime, the key for developers is to remember is that despite the availability of new approaches, good design remains essential and Jacob Nielson's Ten Usability Heuristics [2] should be kept in mind. AJAX applications need to be tested to deal with the idiosyncrasies of different browsers, platforms and usability issues and applications should degrade gracefully for those users who do not have JavaScript enabled.
Note that as the use of AJAX increases and more programming libraries become available, many of the issues will be resolved. In parallel it is likely that over time browsers will standardise and incorporate better support for new technologies.
References
- An Introduction To AJAX, Cultural Heritage briefing document no. 43, UKOLN,
<http://www.ukoln.ac.uk/cultural-heritage/documents/briefing-43/> - Ten Usability Heuristics), Useit.com,
<http://www.useit.com/papers/heuristic/heuristic_list.html>
