I often have to put spinners in places with different backgrounds so a solution that doesn’t involve having to create a separate GIF for each and every single one of these places definitely gets my attention. And spin.js definitely shines in this department with no dependencies to other JS libraries and lots of customizability so that even if you need spinners of multiple sizes on one page, all you have to do is include spin.js, create a new instance of the Spinner with a couple of options for each spinner and be done with it. And if you don’t know what all these options mean, the project’s website has a nice configurator for you.
spin.js does all this by creating multiple div-elements and using CSS translations and animations to make them rotate. For IE it falls back to VML objects.
spin.js is most likely not the one-size-fits-all solution right now but it’s getting really close. One downside of this compared to an animated GIF is that it requires more CPU power especially in IE according to this issue. Especially on modern browsers it probably just a matter of time until CSS animations have been optimized, though.
Another advantage of GIFs is that you can easily just use them as background image (which is probably the preferred way to do it anyway). For instance if you want to add a spinner right into a button (<input type=“submit”> for backwards-compatibility) using a background image is easier than extending the padding of the button and absolutely positioning the spinner on top of that newly created space.
But for everything else I will probably look at spin.js first the next time I need a spinner somewhere. It looks like a great addition to the toolbox of every web developer :D