jquery 实现 返回顶部

//Html代码：

<div class="backToTop" title="返回顶部">返回顶部</div>

//代码
//CSS代码：

.backToTop {    display: none;    width: 18px;    line-height: 1.2;
    padding: 5px ;
    background-color: #;
    color: #fff;
    font-size: 12px;
    text-align: center;
    position: fixed;
    _position: absolute;
    right: 10px;
    bottom: 100px;
    _bottom: "auto";
    cursor: pointer;
    opacity: .;
    filter: Alpha(opacity=);
}

//JS代码：

(function() {

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