// javascript document
/**
@ 回到页面顶部  
@ 2011-12-16
**/
$(function(){

    (function(w, n) {
        var obj=document.getelementbyid("gotopbtn");
        function m(op) {
            var step = op.step || 10; //动画的帧频(ms)
            var time = op.time || 50; //动画的帧数
            var stime = 0;
            document.getelementbyid(op.handle).onclick = function() {
               
                var top = g();
                if(top > 0) {
                    stime = 0;
                    (function() {
                        s(math.ceil(t(stime, top, -top, time)));
                        if(stime < time) {
                            stime++;
                            settimeout(arguments.callee, step);
                        }
                    })();

                }
            };
        }
        //缓动算法
        function t(t, b, c, d) {
            return -c *(t/=d)*(t-2) + b;
        }
        //获取页面scrolltop
        function g() {
            //ff / chrome safari / ie
            return document.documentelement.scrolltop || window.pageyoffset || document.body.scrolltop;
        }
        //设置页面scrolltop
        function s(n) {
            //chrome safari / ff / ie
            (/(chrome|version)/i).test(navigator.useragent)? document.body.scrolltop = n : document.documentelement? document.documentelement.scrolltop = n : document.body.scrolltop = n;
        }

        window.onscroll=function(){g()>300?obj.style.display="block":obj.style.display="block";}

        w[n] = m;
    })(window, 'gomalltop');

//调用   time 为时间
    gomalltop({handle: "gotopbtn", time: 10});

})