Why is it that web apps very often lack something that we take for granted in most window applications, namely the undo function? Is it because it’s not needed? Is it too hard to implement or is it simply just because it’s something that developers don’t think is needed?

The most common solution to prevent user errors is to simply throw an alertbox warning about potential damage or loss of data that the action might cause. Even otherwise awesome web applications often resorts to this behavior. Take for example Backpack from 37 signals, which I regard a very usable and overall great product. When you try to delete a note they throw this alert in your face:

This is, from the developers point of view, the easiest way to handle it. It’s almost too easy to implement an alert and many developers habitually do it without giving it a second thought.

A far better solution is to use an undo function. Although harder to implement it maps so much better to the users mental model and behavior patterns. As Alan Cooper puts it in About Face 3:

Users generally don’t believe, or at least don’t want to believe, that they make mistakes. This is another way of saying that the persona’s mental model typically doesn’t include error on his part. Following a persona’s mental model means absolving him of blame. The implementation model, however, is based on an error-free CPU. Following the implementation model means proposing that all culpability must rest with the user. Thus, most software assumes that it is blameless, and any problems are purely the fault of the user.
Alan Cooper, Aboute Face 3

An undo function enables the user to easily recover from mistakes and also encourage him to explore the interface without fear of doing irreversible damage. It transfers the responsibility of handling errors from the user to the system, where it righteously belongs.

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