Custom fadeTo.

gistfile1.js

// Like the fadeTo from jQuery, but doesn't wait until the previous
// animation is over.
var fadeTo = (function() {
var fadingStep = 13;
return function(jqSel, time, toOpacity) {
	jqSel.each(function(i, elem) {
		if (elem.fadingState != null) {
			clearInterval(elem.fadingState.interval);
		}

		elem.fadingState = {elem: elem, toOpacity: toOpacity, time: time, 
			interval: setInterval(function() {
				var st = elem.fadingState;
				var el = $(elem);
				var currOpacity = parseFloat(el.css('opacity'));
				var rest = toOpacity - currOpacity;
				newOp = currOpacity + (rest / (st.time / 13));
				if (Math.abs(newOp-toOpacity) >= Math.abs(rest)) {
					clearInterval(st.interval);
					delete elem['fadingState'];
					return;
				}
				el.css('opacity', newOp);
				st.time -= fadingStep;
			}, fadingStep),
		}
	});
}
})();