使用onepage_scroll插件时，在JQuery中获取滚动位置

我正在为一个网站使用很棒的onepage_scroll插件。低于设定的阈值，页面将恢复到正常滚动行为。然而，在这一点上，当我尝试使用scrollTop（）来获取离页面顶部的距离时，它总是返回0。

var vph = $(window).height();
var responsiveThreshold = 640;
$(".onepage_scroll").onepage_scroll({
   sectionContainer: "section",     // sectionContainer accepts any kind of selector in case you don't want to use section
   easing: "ease",                  // Easing options accepts the CSS3 easing animation such "ease", "linear", "ease-in", 
                                    // "ease-out", "ease-in-out", or even cubic bezier value such as "cubic-bezier(0.175, 0.885, 0.420, 1.310)"
   animationTime: 1000,             // AnimationTime let you define how long each section takes to animate
   pagination: false,                // You can either show or hide the pagination. Toggle true for show, false for hide.
   updateURL: true,                // Toggle this true if you want the URL to be updated automatically when the user scroll to each page.
   beforeMove: scrollCatchBefore,  // This option accepts a callback function. The function will be called before the page moves.
   afterMove: scrollCatchAfter,   // This option accepts a callback function. The function will be called after the page moves.
   loop: false,                     // You can have the page loop back to the top/bottom when the user navigates at up/down on the first/last page.
   keyboard: true,                  // You can activate the keyboard controls
   responsiveFallback: responsiveThreshold        // You can fallback to normal page scroll by defining the width of the browser in which
                                    // you want the responsive fallback to be triggered. For example, set this to 600 and whenever 
                                    // the browser's width is less than 600, the fallback will kick in.
});


// Fix menu if page is too small
if(vpw<responsiveThreshold) {
    $("#navigation").hide();
    /* Every time the window is scrolled ... */
    $('body').scroll( function(){
        var scrollPos = $('html').scrollTop();
        console.log(vph);
        console.log(scrollPos);
        if(scrollPos > vph) {
            $("#navigation").fadeIn();
        } else {
            $("#navigation").fadeOut();
        }
    });
}

我还尝试了以下两种方法：

$('body').scrollTop();
$('.onepage_scroll').scrollTop();
$(window).scrollTop();