Simple Pulse Animation with jQuery

The simplest way that I could think of to implement a “pulse” effect in jQuery. I know there are plugins that will do this. Not sure that any of them will do it in 12 lines of code.

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I use it to animate an HTML5 drag-and-drop target, wired up to the dragenter event like this:

Update: demo at  http://newbrightidea.com/demos/pulsar