jQuery.fn.goToTop = function(settings) {
    settings = jQuery.extend({
        min: 1,  //距離頂端的最小值為1
        fadeSpeed: 200,  //淡入速度
        ieOffset: 50  //IE相容性問題
    },settings);
    return this.each(function(){
        //listen for scroll
        var el = $(this);
        el.css("display","none");//in case the user forgot
        $(window).scroll(function(){
            //stupid IE hack
            if(!jQuery.support.hrefNormalized) {
                el.css({
                    "position": "absolute",
                    "top" : $(window).scrollTop() + $(window).height() - settings.ieOffset -30
                });
            }

            if($(window).scrollTop() >= settings.min) {
                el.fadeIn(settings.fadeSpeed);
            } else {
                el.fadeOut(settings.fadeSpeed);
            }
        });
    });
};


$(function(){
    var goToTopButton = "<div id='goToTop'><a href='#'></a></div>";
    $(".pane").append(goToTopButton);
    //距離頂端的距離小於showDistance就隱藏goToTop按鈕
    if($(window).scrollTop() < 400) {
        $("#goToTop").hide();
    }
    
    $("#goToTop").goToTop({
        min:300,
        fadeSpeed: 500
    });

    $("#goToTop").click(function(e){
        e.preventDefault();
        $("html,body").animate({scrollTop:0},"slow");
    });
});