web/_javascript/commons/scroll-helper.js

/**
 * A tool for smooth scrolling and topbar switcher
 */
const ScrollHelper = (function () {
    const $body = $("body");
    const ATTR_TOPBAR_VISIBLE = "data-topbar-visible";
    const topbarHeight = $("#topbar-wrapper").outerHeight();

    let scrollUpCount = 0; // the number of times the scroll up was triggered by ToC or anchor
    let topbarLocked = false;
    let orientationLocked = false;

    return {
        hideTopbar: () => $body.attr(ATTR_TOPBAR_VISIBLE, false),
        showTopbar: () => $body.attr(ATTR_TOPBAR_VISIBLE, true),

        // scroll up

        addScrollUpTask: () => {
            scrollUpCount += 1;
            if (!topbarLocked) {
                topbarLocked = true;
            }
        },
        popScrollUpTask: () => scrollUpCount -= 1,
        hasScrollUpTask: () => scrollUpCount > 0,
        topbarLocked: () => topbarLocked === true,
        unlockTopbar: () => topbarLocked = false,
        getTopbarHeight: () => topbarHeight,

        // orientation change

        orientationLocked: () => orientationLocked === true,
        lockOrientation: () => orientationLocked = true,
        unLockOrientation: () => orientationLocked = false
    };

}());