Reacting immediately to the user is not only needed for lookup patterns, but in order to provide interactive feedback in other situations. There are several patterns that help keep the user informed about what is happening in the application:
A Live Preview gives the users a glimpse beforehand of how the application will interpret their input once submitted.
We mentioned Jakob Nielson's Error Prevention principle earlier. This principle says:
Even better than good error messages is a careful design which prevents a problem from occurring in the first place.
Benjamin Franklin seemed to be speaking about the same principle when he uttered the famous quote, "An ounce of prevention is worth a pound of cure."
Use Live Previews to prevent errors.
Being reactive to user input is an excellent way to provide that ounce of prevention. Live Previews dispense just the right amount of information, in context and just in time to keep users informed, preventing unnecessary mistakes.
Wundrbar.com is an example of an interface that reacts immediately (Figure 14-1). Wundrbar provides a search layer to a number of third-party services such as purchasing flight tickets, renting cars, or checking gas prices in Des Moines.
Figure 14-1. Wundrbar provides an immediate reaction to each user input