JS: goTop(smooth move)

JS:UX-goTop(smooth move)

$(document).ready(function() {
    $('.goto-top').click(function(event) {
        event.preventDefault();
        move(documentScrollTop());
        //window.scrollTo(0, 0);
    });
});

//获取或设置文档对象的scrollTop
//function([val])
function documentScrollTop(val){
    var elem = document; 
    return (val!== undefined) ? 
        elem.documentElement.scrollTop = elem.body.scrollTop = val :
        Math.max(elem.documentElement.scrollTop, elem.body.scrollTop);
}

//减速移动滚动条
function move(scrollTop){
    setTimeout(function(){
        scrollTop = Math.floor((scrollTop * 0.65));
        documentScrollTop(scrollTop);
        if(scrollTop !=0 ){
            setTimeout(arguments.callee, 25);
        }
    }, 25);
}

// 滚动时候, 是否显示gotoTop
function scrollHandler(event) {
    var $gotoTop = $('.goto-top');

    if ($(window).scrollTop() > 0) {
        if (!visible) {
            if (isIE6) {
                if ($gotoTop.css('position') != 'absolute') {
                    $gotoTop.css({
                        position: 'absolute'
                    });
                    $gotoTop[0].style.setExpression("top", "eval(document.documentElement.scrollTop + documentElement.clientHeight - this.clientHeight - 40) + 'px'");
                }
            }
            else {
                if ($gotoTop.css('position') != 'fixed') {
                    $gotoTop.css({position: 'fixed'});
                }
            }
            visible = true;
            isIE6 ? $gotoTop.show() : $gotoTop.fadeIn('slow');
        }
    }
    else {
        if (visible) {

            visible = false;
            if(isIE6){
                $gotoTop.css({position: 'relative'});
                $gotoTop.hide();    
            }
            else{
                $gotoTop.fadeOut('fast',function(){
                    $gotoTop.css({position: 'relative'});   
                }); 
            }
            //isIE6 ? $gotoTop.hide() : $gotoTop.fadeOut('slow');
            
        }
    }
}

$(window).scroll(Utils.buffer(scrollHandler, 200));