static/js/toc.js


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var spy = function () {
    var elems = $(":header");
    if (elems.length == 0) {
        return;
    }
    var currentTop = $(window).scrollTop();
    var currentBottom = $(window).scrollTop() + $(window).height();
    var pageBottom = $('#EOF').offset().top;

    var meetUnread = false
    var currentIndex = -1
    elems.each(function (idx) {
        var elemTop = $(this).offset().top;
        var id = $(this).attr('id');
        var navElem = $('#' + id + '-nav');
        if (currentTop + $(this).height() >= elemTop || currentBottom >= pageBottom) {
            navElem.addClass('toc-active');
        } else {
            if (meetUnread == false) {
                meetUnread = true
                currentIndex = idx - 1
            }
            navElem.removeClass('toc-active');
        }
    })
    if (currentIndex == -1) {
        currentIndex = elems.length - 1;
    }
    //console.log(elems[currentIndex].id);
    //Collapse them
    collapseOthers("#" + elems[currentIndex].id + "-nav");
}
var collapseOthers = function (currentId) {
    //console.log(currentId);
    $(currentId).parents(".collapse").each(function (idx) {
        $(this).collapse("show");
    });
    $(currentId).parent().next().filter(".collapse").collapse("show");
    $(".collapse").not($(currentId).parents()).not($(currentId).parent().next()).each(function (idx) {
        $(this).collapse("hide");
    });

}
$().ready(function () {
    spy();
    $(window).bind('scroll', debounce(spy));
});

function debounce(func, delay = 250) {
    let timer = null;

    return () => {
        let context = this;
        let args = arguments;

        clearTimeout(timer);
        timer = setTimeout(() => {
            func.apply(context, args);
        }, delay)
    }
}