原生计算浏览器高度

EventUtil.addHandler(window,'scroll',function(){



	var dafid = document.getElementById('dafid'),

		eletop = dafid.getBoundingClientRect().top;

		if(eletop-549 <= 0){

			dafid.className = 'daf';

		}else{

			dafid.className = '';

		}



});