scrollFollow 滚动跟随该 jQeury插件

该插件可实现在向下拉动时，保持某个DIV一直固定在顶部

      $.fn.extend({
        	scrollFollow:function(settings){
		settings=settings||{};
		settings.container=settings.container||$(this).parent();
		settings.bottomObj=settings.bottomObj||'';
		settings.bottomMargin=settings.bottomMargin||0;
		settings.marginTop=settings.marginTop||0;
		settings.marginBottom=settings.marginBottom||0;
		settings.zindex=settings.zindex||9999;
		settings.width=settings.width||$(this).width();
		var win=$(window);
		var target=$(this);
		if(target.length<=0 || target.attr('fixed')){
			return
		}
		target.attr('fixed','fixed');
		
		var targetTop=parseInt(target.position().top);
//		alert(target.css('borderTopWidth'));
//		targetTop+=parseInt(target.css('borderTopWidth'))+parseInt(target.css('marginTop'));//在IE 6下出错
		var containerHeight=settings.container.height();
		var targetHeight=target.height();
		if(containerHeight-target.height()>=100){
			//return;
		}
		//e.container.css('height',i+'px');
		var positionValue=target.css("position");
		var topValue=target.css('top');
		var widthValue=target.css('width');
		if(settings.bottomObj==''||$(settings.bottomObj).length<=0){
			var hitBottom=false
		}//快递查询http://www.ickd.cn
		else{
			var hitBottom=true
		}
		win.scroll(function(event){
			var th=targetHeight;//targetHeight
			var ch=containerHeight;
			scrollTop=win.scrollTop();
			topPosition=0;
			if(hitBottom==true){
				var maxTop=$(settings.bottomObj).position().top-settings.marginBottom-settings.marginTop;
				topPosition=Math.min(topPosition,(maxTop-scrollTop)-target.outerHeight(true));
			}
//			$('#demsg').html('scrollTop:'+scrollTop+'  targetTop:'+targetTop+' topPosition:'+topPosition+'  maxTop:'+maxTop);
			if(scrollTop>targetTop-settings.marginTop){
				if(window.XMLHttpRequest){
					target.css({
						position:"fixed",top:topPosition+settings.marginTop,'z-index':settings.zindex,width:settings.width+'px'
					});
					target.siblings('#fix-placeholder').css({
						height:target.height()+'px'
					}).show();
				}
				else{
					target.css({
						position:"absolute",top:scrollTop+topPosition+settings.marginTop+'px','z-index':settings.zindex
					})
				}
			}
			else{
				target.css({
					position:positionValue,top:topValue,width:widthValue
				});
				target.siblings('#fix-placeholder').hide();
			}
		});
		return this
	}
});

具体实例可看 http://www.ickd.cn/outlets/