滚动固定侧边栏

根据屏幕高度、滚动高度、侧边栏自身高度判断，具体实现看代码，知道思路就好了

实现代码

var jWindow = $(window);
jWindow.scroll(function(){
	var scrollheight = jWindow.scrollTop();
	var screenHeight = jWindow.height();
	var sideheight = $('#j_BdSide').height();
	if(scrollHeight + screenHeight > sideheight){
		$('#j_BdSide').css({
			'position' : 'fixed',
			'top' : '-(sideheight - screenHeight)',
			'right' : 0
		});
	}else{
		$('#J_BdSide').css({
			'position' : 'static'
		});
	}
});
//当页面加载的时候触发一次滚动
window.onload = function(){
	jWindow.trigger('scroll');
};
//当窗口尺寸发生变化的时候触发滚动
jWindow.resize = function(){
	jWindow.trigger('scroll');
};