There's a related trick I've recently begun using with progress bars which I plan to turn into a little JS library when I have time. Basically, watching a progress bar fill up makes time pass quickly, but making short-lived progress bars update asynchronously is a huge waste of time. You can use a spinner, but that's less effective. Alternatively, you can make the bar fill in a fixed amount of time, which is a problem if the operation takes longer than expected, because staring at a full progress bar makes time seem to pass even more slowly than nothing at all.

The solution I found was an exponential fill. Say you estimate an operation will take 4 seconds (this can even be hard coded). You show a bar that starts empty, and after 2 seconds, it is halfway full, after 4 seconds, 3/4 full, 6 seconds, 7/8, and so on until the operation completes and the bar disappears. That way, you never end up paused on a full progress bar, and you are still conveying a reasonable estimate to your user, and you never have to write another line of code to update a progress bar.