在网上找到的JavaScript的淡入淡出代码都升级基于jQuery的，抑或不合适的，所以自己写了一份。包括我自己的网站首页的广告轮播也用了这份代码。

var anim = {
	switchTimePicc : 0,
	element : null,
	sss : function (x, y, callback)
	{
		if (x == 1)
		{
			if (y<=anim.switchTimePicc)
			{
				anim.element.style.opacity = y/anim.switchTimePicc;
				setTimeout("anim.sss(" + x + ", " + ++y + ", " + callback.toString() + ")", 1);
			} else {
				callback();
			}
		} else {
			if (y>=0)
			{
				anim.element.style.opacity = y/anim.switchTimePicc;
				setTimeout("anim.sss(" + x + ", " + --y + ", " + callback.toString() + ")", 1);
			} else {
				callback();
			}
		}
	},
	fadeIn : function (time, callback)
	{
		anim.switchTimePicc = time;
		if (callback == undefined)
			callback = function () {};
		anim.sss(1, 0, callback);
	},
	fadeOut : function (time, callback)
	{
		anim.switchTimePicc = time;
		if (callback == undefined)
			callback = function () {};
		anim.sss(2, time, callback);
	}
}