对联浮动广告

JS

window.onload = function(){
	//对联广告单击显示
	document.getElementById("openAbs").onclick = function(){
		var
		coupletAdsLeft = null,
		coupletAdsRight = null,

		coupletAds = function(absLeft, absRight){
			coupletAdsLeft = absLeft;
			coupletAdsRight = absRight;

			this.coupletAdsLeft.style.display = "block";
			this.coupletAdsRight.style.display = "block";
			absTop();
		},

		absTop = function(){//两个对联层的top位置
			if(!this.coupletAdsLeft) return;
			//如果 document.body.scrollTop == 0 选则document.documentElement.scrollTop值，
			var top = ((document.body.scrollTop || document.documentElement.scrollTop) + window.screen.availHeight/2 - this.coupletAdsLeft.offsetHeight) + "px";
			this.coupletAdsLeft.style.top = top;
			this.coupletAdsRight.style.top = top;
		},

		scrollEvent = (function(){//滚轴事件
			window.onscroll = function(){
				absTop();//重新修正广告top
			}
		})();

		coupletAds(
				document.getElementById("coupletAdsLeft"),
				document.getElementById("coupletAdsRight")
		);
	}
};