返回顶部的js实现
(function() {
    var backToTopTxt = "返回顶部", backToTopEle = $('<div class="backToTop tops"></div>').appendTo($("body"))
        .text(backToTopTxt).attr("title", backToTopTxt).click(function() {
            $("html, body").animate({ scrollTop: 0 }, 520);
    }), backToTopFun = function() {
        var st = $(document).scrollTop(), winh = $(window).height();
        (st > 0)? backToTopEle.show(): backToTopEle.hide();   
        //IE6下的定位
        if (!window.XMLHttpRequest) {
            backToTopEle.css("top", st + winh - 60);   
        }
    };
    $(window).bind("scroll", backToTopFun);
    $(function() { backToTopFun(); });
})();