<!-- element we are going to animate -->
<div id="box"> Ninja </div>

<script type="text/javascript">

	function animateIt(elementId) {

		//inside the animateIt() function, we get a reference to that element.
		var elem = document.getElementById(elementId);
		//establishes a counter to keep track of animation ticks (steps)
		var tick = 0;

		//creates and starts an interval timer given a callback function that will be invoked every 10ms.
		//For 100 ticks, it will adjust the position of the element.
		var timer = setInterval(function() {
			if (tick < 100) {
				elem.style.left = elem.style.top = tick + "px";
				tick++;
			}
			else {
				clearInterval(timer);
				assert(tick == 100, "Tick is accessed via a closure");
				assert(elem, "Element also accessed via closure");
				assert(timer, "Timer reference also obtained via closure");
			}
		}, 10);
	}

	animateIt('box');
</script>