//导航固定
	var fixedbox=function(el){
		this.element=el;
		this.boxy=getxy(this.element).y;
	}
	fixedbox.prototype={
		setcss:function(){
			var windowst=(document.compatmode && document.compatmode!="css1compat")? document.body.scrolltop:document.documentelement.scrolltop||window.pageyoffset;
			if(windowst>this.boxy){
				this.element.style.csstext="position:fixed;top:0px;width:100%;z-index:110;left:0px;padding:0px;margin-top:0;opacity:1;background:#fff;border-bottom:0;box-shadow:0px 2px 5px 0px rgba(0,0,0,.15);";
			}else{
				this.element.style.csstext="";
			}
		}
	};
	//添加事件
	function addevent(elm, evtype, fn, usecapture) {
		if (elm.addeventlistener) {
			elm.addeventlistener(evtype, fn, usecapture);
		return true;
		}else if (elm.attachevent) {
			var r = elm.attachevent('on' + evtype, fn);
			return r;
		}
		else {
			elm['on' + evtype] = fn;
		}
	}
	//获取元素的xy坐标；
	function getxy(el) {
        return document.documentelement.getboundingclientrect && (function() {//取元素坐标，如元素或其上层元素设置position relative
            var pos = el.getboundingclientrect();
            return { x: pos.left + document.documentelement.scrollleft, y: pos.top + document.documentelement.scrolltop };
        })() || (function() {
            var _x = 0, _y = 0;
            do {
                _x += el.offsetleft;
                _y += el.offsettop;
            } while (el = el.offsetparent);
            return { x: _x, y: _y };
        })();
    }
	//实例化；
	var diva=new fixedbox(document.getelementbyid("week_nav"));
   	addevent(window,"scroll",function(){
		diva.setcss();
	});