图片轮播特效，jQuery实现

img 中的alt属性作用：当img图片无法显示时，将显示alt中的文字。<span>中index的作用：给这个元素添加一个属性，按照这个属性值给元素排序

jQuery实现

	$(window).scroll(function() {
				// 固定边栏滚动特效
				var windowHeight = $(window).scrollTop() + $(window).height();
				var sideHeight = $('#J_BdSide').height();
				if (windowHeight > sideHeight) {
					$('#J_BdSide').css({
						'position' : 'fixed',
						right : '0px',
						top : -(sideHeight - $(window).height())
					});
				} else {
					$('#J_BdSide').css({
						'position' : 'static'
					});
				}
			});

javascript实现特效：

var $ = function(id){
				return document.getElementById(id);
			}

			var addEvent = function(obj,event,fn){
                if(obj.addEventListener){
                	obj.addEventListener(event,fn,false);
                }else if(obj.attachEvent){
                	obj.attachEvent('on'+event,fn);
                }
			}
			var domSider = $('J_BdSide');
			var scrollEvent = function(){
				var sideHeight = domSider.offsetHeight;
				var screenHeight =document.documentElement.clientHeight||document.body.clientHeight;
				var scrollHeight = document.documentElement.scrollTop||document.body.scrollTop;
				if(scrollHeight+screenHeight>sideHeight){
					domSider.style.cssText = 'position:fixed;right:0px;top:'+(-(sideHeight-screenHeight))+'px';
				}else{
					domSider.style.position='static';
				}
			}
			addEvent(window,'scroll',function(){
				scrollEvent();
				
			});
			addEvent(window,'resize',function(){
				scrollEvent();
			});