Article on Javascript Animation

To make an animation on your computer, we want to move an image in a similar way, but you do not have "frames" to work with. Instead, we have milliseconds in which we can execute commands. We can change what's on the screen every millisecond in order to create the appearance of motion. We don't have to change the screen nearly that fast, though. The human eye can only register motion at a rate of approximately 24 frames per second. Faster than that, and the brain just doesn't recognize the difference. For the ease of calculation, then, it's simple to consider an optimum image change rate or 25 frames/1000 milliseconds. That's the same as saying 1/40, or 1"frame" change every 40 milliseconds.