diff --git a/_javascript/commons/topbar-switch.js b/_javascript/commons/topbar-switch.js
index 1740d1f..b8942dd 100644
--- a/_javascript/commons/topbar-switch.js
+++ b/_javascript/commons/topbar-switch.js
@@ -4,6 +4,7 @@
 
 $(function() {
   const $topbarWrapper = $("#topbar-wrapper");
+  const $topbarTitle = $("#topbar-title");
   const $panel = $("#panel-wrapper");
   const $searchInput = $("#search-input");
 
@@ -54,7 +55,7 @@ $(function() {
   }
 
   $(window).scroll(function(event) {
-    if ($("#topbar-title").is(":hidden")) {
+    if ($topbarTitle.is(":hidden")) {
       didScroll = true;
     }
   });
diff --git a/_javascript/commons/topbar-title.js b/_javascript/commons/topbar-title.js
index 6bc7805..2208afa 100644
--- a/_javascript/commons/topbar-title.js
+++ b/_javascript/commons/topbar-title.js
@@ -1,46 +1,61 @@
 /*
- * Top bar title auto change while scrolling in mobile screens.
+ * Top bar title auto change while scrolling up/down in mobile screens.
 */
 
 $(function() {
+  const titleSelector = "div.post>h1:first-of-type";
+  const $pageTitle = $(titleSelector);
+  const $topbarTitle = $("#topbar-title");
 
-  const topbarTitle = $("#topbar-title");
-  const postTitle = $("div.post>h1");
+  if ($pageTitle.length === 0 /* on Home page */
+      || $pageTitle.hasClass("dynamic-title")
+      || $topbarTitle.is(":hidden")) {/* not in mobile views */
+    return;
+  }
 
-  const DEFAULT = topbarTitle.text().trim();
-
-  let title = (postTitle.length > 0) ?
-    postTitle.text().trim() : $("h1").text().trim();
+  const defaultTitleText = $topbarTitle.text().trim();
+  let titleText = $pageTitle.text().trim();
+  let hasScrolled = false;
+  let lastScrollTop = 0;
 
   if ($("#page-category").length || $("#page-tag").length) {
     /* The title in Category or Tag page will be "<title> <count_of_posts>" */
-    if (/\s/.test(title)) {
-      title = title.replace(/[0-9]/g, "").trim();
+    if (/\s/.test(titleText)) {
+      titleText = titleText.replace(/[0-9]/g, "").trim();
     }
   }
 
-  /* Replace topbar title while scroll screens. */
-  $(window).scroll(function () {
-    if ($("#post-list").length /* in Home page */
-      || postTitle.is(":hidden") /* is tab pages */
-      || topbarTitle.is(":hidden") /* not mobile screens */
-      || $("#sidebar.sidebar-expand").length) { /* when the sidebar trigger is clicked */
-      return false;
+  let options = {
+    rootMargin: '-48px 0px 0px 0px', // 48px equals to the topbar height (3rem)
+    threshold: [0, 1]
+  };
+
+  let observer = new IntersectionObserver((entries) => {
+    if (!hasScrolled) {
+      hasScrolled = true;
+      return;
     }
 
-    if ($(this).scrollTop() >= 95) {
-      if (topbarTitle.text() !== title) {
-        topbarTitle.text(title);
+    let curScrollTop = $(window).scrollTop();
+    let isScrollDown = lastScrollTop < curScrollTop;
+    lastScrollTop = curScrollTop;
+    let heading = entries[0];
+
+    if (isScrollDown) {
+      if (heading.intersectionRatio === 0) {
+        $topbarTitle.text(titleText);
       }
     } else {
-      if (topbarTitle.text() !== DEFAULT) {
-        topbarTitle.text(DEFAULT);
+      if (heading.intersectionRatio === 1) {
+        $topbarTitle.text(defaultTitleText);
       }
     }
-  });
+  }, options);
 
-  /* Click title remove hover effect. */
-  topbarTitle.click(function() {
+  observer.observe(document.querySelector(titleSelector));
+
+  /* Click title will scroll to top */
+  $topbarTitle.click(function() {
     $("body,html").animate({scrollTop: 0}, 800);
   });
 
diff --git a/assets/js/dist/categories.min.js b/assets/js/dist/categories.min.js
index 611e5e8..0c06029 100644
--- a/assets/js/dist/categories.min.js
+++ b/assets/js/dist/categories.min.js
@@ -3,4 +3,4 @@
  * © 2019 Cotes Chung
  * MIT Licensed
  */
-$(function(){$(window).scroll(()=>{50<$(this).scrollTop()&&"none"===$("#sidebar-trigger").css("display")?$("#back-to-top").fadeIn():$("#back-to-top").fadeOut()}),$("#back-to-top").click(()=>($("body,html").animate({scrollTop:0},800),!1))}),$(function(){$(".mode-toggle").click(e=>{const o=$(e.target);let t=o.prop("tagName")==="button".toUpperCase()?o:o.parent();t.blur(),flipMode()})}),$(function(){const e=$("#sidebar-trigger"),o=$("#search-trigger"),t=$("#search-cancel"),s=$("#search-cleaner"),a=$("#main"),l=$("#topbar-title"),r=$("#search-wrapper"),n=$("#search-result-wrapper"),d=$("#search-results"),i=$("#search-input"),c=$("#search-hints"),u=function(){let e=0;return{block(){e=window.scrollY,$("html,body").scrollTop(0)},release(){$("html,body").scrollTop(e)},getOffset(){return e}}}(),f={on(){e.addClass("unloaded"),l.addClass("unloaded"),o.addClass("unloaded"),r.addClass("d-flex"),t.addClass("loaded")},off(){t.removeClass("loaded"),r.removeClass("d-flex"),e.removeClass("unloaded"),l.removeClass("unloaded"),o.removeClass("unloaded")}},p=function(){let e=!1;return{on(){e||(u.block(),n.removeClass("unloaded"),a.addClass("unloaded"),e=!0)},off(){e&&(d.empty(),c.hasClass("unloaded")&&c.removeClass("unloaded"),n.addClass("unloaded"),s.removeClass("visible"),a.removeClass("unloaded"),u.release(),i.val(""),e=!1)},isVisible(){return e}}}();function h(){return t.hasClass("loaded")}o.click(function(){f.on(),p.on(),i.focus()}),t.click(function(){f.off(),p.off()}),i.focus(function(){r.addClass("input-focus")}),i.focusout(function(){r.removeClass("input-focus")}),i.on("keyup",function(e){8===e.keyCode&&""===i.val()?h()?c.removeClass("unloaded"):p.off():""!==i.val()&&(p.on(),s.hasClass("visible")||s.addClass("visible"),h()&&c.addClass("unloaded"))}),s.on("click",function(){i.val(""),h()?(c.removeClass("unloaded"),d.empty()):p.off(),i.focus(),s.removeClass("visible")})}),$(function(){var e=function(){const e="sidebar-display";let o=!1;const t=$("body");return{toggle(){!1===o?t.attr(e,""):t.removeAttr(e),o=!o}}}();$("#sidebar-trigger").click(e.toggle),$("#mask").click(e.toggle)}),$(function(){$('[data-toggle="tooltip"]').tooltip()}),$(function(){const t=$("#topbar-wrapper"),s=$("#panel-wrapper"),a=$("#search-input"),l="topbar-up",r="topbar-down",n="toc-scrolling-up";let o,d=0;const i=t.outerHeight(),c=t.outerHeight();$(window).scroll(function(e){$("#topbar-title").is(":hidden")&&(o=!0)}),setInterval(function(){o&&(function(){var e,o=$(this).scrollTop();Math.abs(d-o)<=i||(o>d?o>c&&(t.removeClass(r).addClass(l),s.removeClass(r),a.is(":focus")&&a.blur()):o+$(window).height()<$(document).height()&&(void 0!==(e=t.attr(n))?"false"===e&&t.removeAttr(n):(t.removeClass(l).addClass(r),s.addClass(r))),d=o)}(),o=!1)},250)}),$(function(){const e=$("#topbar-title"),o=$("div.post>h1"),t=e.text().trim();let s=(0<o.length?o:$("h1")).text().trim();($("#page-category").length||$("#page-tag").length)&&/\s/.test(s)&&(s=s.replace(/[0-9]/g,"").trim()),$(window).scroll(function(){return!($("#post-list").length||o.is(":hidden")||e.is(":hidden")||$("#sidebar.sidebar-expand").length)&&void(95<=$(this).scrollTop()?e.text()!==s&&e.text(s):e.text()!==t&&e.text(t))}),e.click(function(){$("body,html").animate({scrollTop:0},800)})}),$(function(){const e=$(".collapse");e.on("hide.bs.collapse",function(){var e="h_"+$(this).attr("id").substring("l_".length);e&&($(`#${e} .far.fa-folder-open`).attr("class","far fa-folder fa-fw"),$(`#${e} i.fas`).addClass("rotate"),$("#"+e).removeClass("hide-border-bottom"))}),e.on("show.bs.collapse",function(){var e="h_"+$(this).attr("id").substring("l_".length);e&&($(`#${e} .far.fa-folder`).attr("class","far fa-folder-open fa-fw"),$(`#${e} i.fas`).removeClass("rotate"),$("#"+e).addClass("hide-border-bottom"))})});
\ No newline at end of file
+$(function(){$(window).scroll(()=>{50<$(this).scrollTop()&&"none"===$("#sidebar-trigger").css("display")?$("#back-to-top").fadeIn():$("#back-to-top").fadeOut()}),$("#back-to-top").click(()=>($("body,html").animate({scrollTop:0},800),!1))}),$(function(){$(".mode-toggle").click(e=>{const o=$(e.target);let t=o.prop("tagName")==="button".toUpperCase()?o:o.parent();t.blur(),flipMode()})}),$(function(){const e=$("#sidebar-trigger"),o=$("#search-trigger"),t=$("#search-cancel"),s=$("#search-cleaner"),a=$("#main"),l=$("#topbar-title"),r=$("#search-wrapper"),n=$("#search-result-wrapper"),d=$("#search-results"),i=$("#search-input"),c=$("#search-hints"),u=function(){let e=0;return{block(){e=window.scrollY,$("html,body").scrollTop(0)},release(){$("html,body").scrollTop(e)},getOffset(){return e}}}(),f={on(){e.addClass("unloaded"),l.addClass("unloaded"),o.addClass("unloaded"),r.addClass("d-flex"),t.addClass("loaded")},off(){t.removeClass("loaded"),r.removeClass("d-flex"),e.removeClass("unloaded"),l.removeClass("unloaded"),o.removeClass("unloaded")}},p=function(){let e=!1;return{on(){e||(u.block(),n.removeClass("unloaded"),a.addClass("unloaded"),e=!0)},off(){e&&(d.empty(),c.hasClass("unloaded")&&c.removeClass("unloaded"),n.addClass("unloaded"),s.removeClass("visible"),a.removeClass("unloaded"),u.release(),i.val(""),e=!1)},isVisible(){return e}}}();function h(){return t.hasClass("loaded")}o.click(function(){f.on(),p.on(),i.focus()}),t.click(function(){f.off(),p.off()}),i.focus(function(){r.addClass("input-focus")}),i.focusout(function(){r.removeClass("input-focus")}),i.on("keyup",function(e){8===e.keyCode&&""===i.val()?h()?c.removeClass("unloaded"):p.off():""!==i.val()&&(p.on(),s.hasClass("visible")||s.addClass("visible"),h()&&c.addClass("unloaded"))}),s.on("click",function(){i.val(""),h()?(c.removeClass("unloaded"),d.empty()):p.off(),i.focus(),s.removeClass("visible")})}),$(function(){var e=function(){const e="sidebar-display";let o=!1;const t=$("body");return{toggle(){!1===o?t.attr(e,""):t.removeAttr(e),o=!o}}}();$("#sidebar-trigger").click(e.toggle),$("#mask").click(e.toggle)}),$(function(){$('[data-toggle="tooltip"]').tooltip()}),$(function(){const t=$("#topbar-wrapper"),o=$("#topbar-title"),s=$("#panel-wrapper"),a=$("#search-input"),l="topbar-up",r="topbar-down",n="toc-scrolling-up";let d,i=0;const c=t.outerHeight(),u=t.outerHeight();$(window).scroll(function(e){o.is(":hidden")&&(d=!0)}),setInterval(function(){d&&(function(){var e,o=$(this).scrollTop();Math.abs(i-o)<=c||(o>i?o>u&&(t.removeClass(r).addClass(l),s.removeClass(r),a.is(":focus")&&a.blur()):o+$(window).height()<$(document).height()&&(void 0!==(e=t.attr(n))?"false"===e&&t.removeAttr(n):(t.removeClass(l).addClass(r),s.addClass(r))),i=o)}(),d=!1)},250)}),$(function(){var o="div.post>h1:first-of-type";const t=$(o),r=$("#topbar-title");if(0!==t.length&&!t.hasClass("dynamic-title")&&!r.is(":hidden")){const n=r.text().trim();let s=t.text().trim(),a=!1,l=0;($("#page-category").length||$("#page-tag").length)&&/\s/.test(s)&&(s=s.replace(/[0-9]/g,"").trim());let e=new IntersectionObserver(e=>{var o,t;a?(o=$(window).scrollTop(),t=l<o,l=o,e=e[0],t?0===e.intersectionRatio&&r.text(s):1===e.intersectionRatio&&r.text(n)):a=!0},{rootMargin:"-48px 0px 0px 0px",threshold:[0,1]});e.observe(document.querySelector(o)),r.click(function(){$("body,html").animate({scrollTop:0},800)})}}),$(function(){const e=$(".collapse");e.on("hide.bs.collapse",function(){var e="h_"+$(this).attr("id").substring("l_".length);e&&($(`#${e} .far.fa-folder-open`).attr("class","far fa-folder fa-fw"),$(`#${e} i.fas`).addClass("rotate"),$("#"+e).removeClass("hide-border-bottom"))}),e.on("show.bs.collapse",function(){var e="h_"+$(this).attr("id").substring("l_".length);e&&($(`#${e} .far.fa-folder`).attr("class","far fa-folder-open fa-fw"),$(`#${e} i.fas`).removeClass("rotate"),$("#"+e).addClass("hide-border-bottom"))})});
\ No newline at end of file
diff --git a/assets/js/dist/commons.min.js b/assets/js/dist/commons.min.js
index 5ea9898..ce404e7 100644
--- a/assets/js/dist/commons.min.js
+++ b/assets/js/dist/commons.min.js
@@ -3,4 +3,4 @@
  * © 2019 Cotes Chung
  * MIT Licensed
  */
-$(function(){$(window).scroll(()=>{50<$(this).scrollTop()&&"none"===$("#sidebar-trigger").css("display")?$("#back-to-top").fadeIn():$("#back-to-top").fadeOut()}),$("#back-to-top").click(()=>($("body,html").animate({scrollTop:0},800),!1))}),$(function(){$(".mode-toggle").click(e=>{const o=$(e.target);let t=o.prop("tagName")==="button".toUpperCase()?o:o.parent();t.blur(),flipMode()})}),$(function(){const e=$("#sidebar-trigger"),o=$("#search-trigger"),t=$("#search-cancel"),s=$("#search-cleaner"),l=$("#main"),a=$("#topbar-title"),n=$("#search-wrapper"),r=$("#search-result-wrapper"),d=$("#search-results"),i=$("#search-input"),c=$("#search-hints"),u=function(){let e=0;return{block(){e=window.scrollY,$("html,body").scrollTop(0)},release(){$("html,body").scrollTop(e)},getOffset(){return e}}}(),p={on(){e.addClass("unloaded"),a.addClass("unloaded"),o.addClass("unloaded"),n.addClass("d-flex"),t.addClass("loaded")},off(){t.removeClass("loaded"),n.removeClass("d-flex"),e.removeClass("unloaded"),a.removeClass("unloaded"),o.removeClass("unloaded")}},f=function(){let e=!1;return{on(){e||(u.block(),r.removeClass("unloaded"),l.addClass("unloaded"),e=!0)},off(){e&&(d.empty(),c.hasClass("unloaded")&&c.removeClass("unloaded"),r.addClass("unloaded"),s.removeClass("visible"),l.removeClass("unloaded"),u.release(),i.val(""),e=!1)},isVisible(){return e}}}();function h(){return t.hasClass("loaded")}o.click(function(){p.on(),f.on(),i.focus()}),t.click(function(){p.off(),f.off()}),i.focus(function(){n.addClass("input-focus")}),i.focusout(function(){n.removeClass("input-focus")}),i.on("keyup",function(e){8===e.keyCode&&""===i.val()?h()?c.removeClass("unloaded"):f.off():""!==i.val()&&(f.on(),s.hasClass("visible")||s.addClass("visible"),h()&&c.addClass("unloaded"))}),s.on("click",function(){i.val(""),h()?(c.removeClass("unloaded"),d.empty()):f.off(),i.focus(),s.removeClass("visible")})}),$(function(){var e=function(){const e="sidebar-display";let o=!1;const t=$("body");return{toggle(){!1===o?t.attr(e,""):t.removeAttr(e),o=!o}}}();$("#sidebar-trigger").click(e.toggle),$("#mask").click(e.toggle)}),$(function(){$('[data-toggle="tooltip"]').tooltip()}),$(function(){const t=$("#topbar-wrapper"),s=$("#panel-wrapper"),l=$("#search-input"),a="topbar-up",n="topbar-down",r="toc-scrolling-up";let o,d=0;const i=t.outerHeight(),c=t.outerHeight();$(window).scroll(function(e){$("#topbar-title").is(":hidden")&&(o=!0)}),setInterval(function(){o&&(function(){var e,o=$(this).scrollTop();Math.abs(d-o)<=i||(o>d?o>c&&(t.removeClass(n).addClass(a),s.removeClass(n),l.is(":focus")&&l.blur()):o+$(window).height()<$(document).height()&&(void 0!==(e=t.attr(r))?"false"===e&&t.removeAttr(r):(t.removeClass(a).addClass(n),s.addClass(n))),d=o)}(),o=!1)},250)}),$(function(){const e=$("#topbar-title"),o=$("div.post>h1"),t=e.text().trim();let s=(0<o.length?o:$("h1")).text().trim();($("#page-category").length||$("#page-tag").length)&&/\s/.test(s)&&(s=s.replace(/[0-9]/g,"").trim()),$(window).scroll(function(){return!($("#post-list").length||o.is(":hidden")||e.is(":hidden")||$("#sidebar.sidebar-expand").length)&&void(95<=$(this).scrollTop()?e.text()!==s&&e.text(s):e.text()!==t&&e.text(t))}),e.click(function(){$("body,html").animate({scrollTop:0},800)})});
\ No newline at end of file
+$(function(){$(window).scroll(()=>{50<$(this).scrollTop()&&"none"===$("#sidebar-trigger").css("display")?$("#back-to-top").fadeIn():$("#back-to-top").fadeOut()}),$("#back-to-top").click(()=>($("body,html").animate({scrollTop:0},800),!1))}),$(function(){$(".mode-toggle").click(e=>{const o=$(e.target);let t=o.prop("tagName")==="button".toUpperCase()?o:o.parent();t.blur(),flipMode()})}),$(function(){const e=$("#sidebar-trigger"),o=$("#search-trigger"),t=$("#search-cancel"),s=$("#search-cleaner"),a=$("#main"),l=$("#topbar-title"),n=$("#search-wrapper"),r=$("#search-result-wrapper"),i=$("#search-results"),d=$("#search-input"),c=$("#search-hints"),u=function(){let e=0;return{block(){e=window.scrollY,$("html,body").scrollTop(0)},release(){$("html,body").scrollTop(e)},getOffset(){return e}}}(),p={on(){e.addClass("unloaded"),l.addClass("unloaded"),o.addClass("unloaded"),n.addClass("d-flex"),t.addClass("loaded")},off(){t.removeClass("loaded"),n.removeClass("d-flex"),e.removeClass("unloaded"),l.removeClass("unloaded"),o.removeClass("unloaded")}},f=function(){let e=!1;return{on(){e||(u.block(),r.removeClass("unloaded"),a.addClass("unloaded"),e=!0)},off(){e&&(i.empty(),c.hasClass("unloaded")&&c.removeClass("unloaded"),r.addClass("unloaded"),s.removeClass("visible"),a.removeClass("unloaded"),u.release(),d.val(""),e=!1)},isVisible(){return e}}}();function m(){return t.hasClass("loaded")}o.click(function(){p.on(),f.on(),d.focus()}),t.click(function(){p.off(),f.off()}),d.focus(function(){n.addClass("input-focus")}),d.focusout(function(){n.removeClass("input-focus")}),d.on("keyup",function(e){8===e.keyCode&&""===d.val()?m()?c.removeClass("unloaded"):f.off():""!==d.val()&&(f.on(),s.hasClass("visible")||s.addClass("visible"),m()&&c.addClass("unloaded"))}),s.on("click",function(){d.val(""),m()?(c.removeClass("unloaded"),i.empty()):f.off(),d.focus(),s.removeClass("visible")})}),$(function(){var e=function(){const e="sidebar-display";let o=!1;const t=$("body");return{toggle(){!1===o?t.attr(e,""):t.removeAttr(e),o=!o}}}();$("#sidebar-trigger").click(e.toggle),$("#mask").click(e.toggle)}),$(function(){$('[data-toggle="tooltip"]').tooltip()}),$(function(){const t=$("#topbar-wrapper"),o=$("#topbar-title"),s=$("#panel-wrapper"),a=$("#search-input"),l="topbar-up",n="topbar-down",r="toc-scrolling-up";let i,d=0;const c=t.outerHeight(),u=t.outerHeight();$(window).scroll(function(e){o.is(":hidden")&&(i=!0)}),setInterval(function(){i&&(function(){var e,o=$(this).scrollTop();Math.abs(d-o)<=c||(o>d?o>u&&(t.removeClass(n).addClass(l),s.removeClass(n),a.is(":focus")&&a.blur()):o+$(window).height()<$(document).height()&&(void 0!==(e=t.attr(r))?"false"===e&&t.removeAttr(r):(t.removeClass(l).addClass(n),s.addClass(n))),d=o)}(),i=!1)},250)}),$(function(){var o="div.post>h1:first-of-type";const t=$(o),n=$("#topbar-title");if(0!==t.length&&!t.hasClass("dynamic-title")&&!n.is(":hidden")){const r=n.text().trim();let s=t.text().trim(),a=!1,l=0;($("#page-category").length||$("#page-tag").length)&&/\s/.test(s)&&(s=s.replace(/[0-9]/g,"").trim());let e=new IntersectionObserver(e=>{var o,t;a?(o=$(window).scrollTop(),t=l<o,l=o,e=e[0],t?0===e.intersectionRatio&&n.text(s):1===e.intersectionRatio&&n.text(r)):a=!0},{rootMargin:"-48px 0px 0px 0px",threshold:[0,1]});e.observe(document.querySelector(o)),n.click(function(){$("body,html").animate({scrollTop:0},800)})}});
\ No newline at end of file
diff --git a/assets/js/dist/home.min.js b/assets/js/dist/home.min.js
index 55576d2..4e3b29b 100644
--- a/assets/js/dist/home.min.js
+++ b/assets/js/dist/home.min.js
@@ -3,4 +3,4 @@
  * © 2019 Cotes Chung
  * MIT Licensed
  */
-$(function(){$(window).scroll(()=>{50<$(this).scrollTop()&&"none"===$("#sidebar-trigger").css("display")?$("#back-to-top").fadeIn():$("#back-to-top").fadeOut()}),$("#back-to-top").click(()=>($("body,html").animate({scrollTop:0},800),!1))}),$(function(){$(".mode-toggle").click(t=>{const e=$(t.target);let o=e.prop("tagName")==="button".toUpperCase()?e:e.parent();o.blur(),flipMode()})}),$(function(){const t=$("#sidebar-trigger"),e=$("#search-trigger"),o=$("#search-cancel"),a=$("#search-cleaner"),s=$("#main"),l=$("#topbar-title"),n=$("#search-wrapper"),r=$("#search-result-wrapper"),i=$("#search-results"),d=$("#search-input"),c=$("#search-hints"),u=function(){let t=0;return{block(){t=window.scrollY,$("html,body").scrollTop(0)},release(){$("html,body").scrollTop(t)},getOffset(){return t}}}(),p={on(){t.addClass("unloaded"),l.addClass("unloaded"),e.addClass("unloaded"),n.addClass("d-flex"),o.addClass("loaded")},off(){o.removeClass("loaded"),n.removeClass("d-flex"),t.removeClass("unloaded"),l.removeClass("unloaded"),e.removeClass("unloaded")}},f=function(){let t=!1;return{on(){t||(u.block(),r.removeClass("unloaded"),s.addClass("unloaded"),t=!0)},off(){t&&(i.empty(),c.hasClass("unloaded")&&c.removeClass("unloaded"),r.addClass("unloaded"),a.removeClass("visible"),s.removeClass("unloaded"),u.release(),d.val(""),t=!1)},isVisible(){return t}}}();function h(){return o.hasClass("loaded")}e.click(function(){p.on(),f.on(),d.focus()}),o.click(function(){p.off(),f.off()}),d.focus(function(){n.addClass("input-focus")}),d.focusout(function(){n.removeClass("input-focus")}),d.on("keyup",function(t){8===t.keyCode&&""===d.val()?h()?c.removeClass("unloaded"):f.off():""!==d.val()&&(f.on(),a.hasClass("visible")||a.addClass("visible"),h()&&c.addClass("unloaded"))}),a.on("click",function(){d.val(""),h()?(c.removeClass("unloaded"),i.empty()):f.off(),d.focus(),a.removeClass("visible")})}),$(function(){var t=function(){const t="sidebar-display";let e=!1;const o=$("body");return{toggle(){!1===e?o.attr(t,""):o.removeAttr(t),e=!e}}}();$("#sidebar-trigger").click(t.toggle),$("#mask").click(t.toggle)}),$(function(){$('[data-toggle="tooltip"]').tooltip()}),$(function(){const o=$("#topbar-wrapper"),a=$("#panel-wrapper"),s=$("#search-input"),l="topbar-up",n="topbar-down",r="toc-scrolling-up";let e,i=0;const d=o.outerHeight(),c=o.outerHeight();$(window).scroll(function(t){$("#topbar-title").is(":hidden")&&(e=!0)}),setInterval(function(){e&&(function(){var t,e=$(this).scrollTop();Math.abs(i-e)<=d||(e>i?e>c&&(o.removeClass(n).addClass(l),a.removeClass(n),s.is(":focus")&&s.blur()):e+$(window).height()<$(document).height()&&(void 0!==(t=o.attr(r))?"false"===t&&o.removeAttr(r):(o.removeClass(l).addClass(n),a.addClass(n))),i=e)}(),e=!1)},250)}),$(function(){const t=$("#topbar-title"),e=$("div.post>h1"),o=t.text().trim();let a=(0<e.length?e:$("h1")).text().trim();($("#page-category").length||$("#page-tag").length)&&/\s/.test(a)&&(a=a.replace(/[0-9]/g,"").trim()),$(window).scroll(function(){return!($("#post-list").length||e.is(":hidden")||t.is(":hidden")||$("#sidebar.sidebar-expand").length)&&void(95<=$(this).scrollTop()?t.text()!==a&&t.text(a):t.text()!==o&&t.text(o))}),t.click(function(){$("body,html").animate({scrollTop:0},800)})}),$(function(){let o=$(".timeago").length,t=void 0;const s=$("meta[name=day-prompt]").attr("content"),l=$("meta[name=hour-prompt]").attr("content"),n=$("meta[name=minute-prompt]").attr("content"),r=$("meta[name=justnow-prompt]").attr("content");function e(){return $(".timeago").each(function(){var t,e;!1!==$(this)[0].hasAttribute("date")?(e=function(t,e){let o=new Date,a=new Date(t);return a.getFullYear()!==o.getFullYear()||a.getMonth()!==o.getMonth()?e:(t=Math.floor((o-a)/1e3),1<=(e=Math.floor(t/86400))?` ${e} `+s:1<=(e=Math.floor(t/3600))?` ${e} `+l:1<=(t=Math.floor(t/60))?` ${t} `+n:r)}($(this).attr("date"),t=$(this).text()))===t?$(this).removeAttr("date"):$(this).text(e):--o}),0===o&&void 0!==t&&clearInterval(t),o}0!==o&&0<e()&&(t=setInterval(e,6e4))});
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+$(function(){$(window).scroll(()=>{50<$(this).scrollTop()&&"none"===$("#sidebar-trigger").css("display")?$("#back-to-top").fadeIn():$("#back-to-top").fadeOut()}),$("#back-to-top").click(()=>($("body,html").animate({scrollTop:0},800),!1))}),$(function(){$(".mode-toggle").click(t=>{const e=$(t.target);let o=e.prop("tagName")==="button".toUpperCase()?e:e.parent();o.blur(),flipMode()})}),$(function(){const t=$("#sidebar-trigger"),e=$("#search-trigger"),o=$("#search-cancel"),a=$("#search-cleaner"),s=$("#main"),l=$("#topbar-title"),n=$("#search-wrapper"),r=$("#search-result-wrapper"),i=$("#search-results"),d=$("#search-input"),c=$("#search-hints"),u=function(){let t=0;return{block(){t=window.scrollY,$("html,body").scrollTop(0)},release(){$("html,body").scrollTop(t)},getOffset(){return t}}}(),p={on(){t.addClass("unloaded"),l.addClass("unloaded"),e.addClass("unloaded"),n.addClass("d-flex"),o.addClass("loaded")},off(){o.removeClass("loaded"),n.removeClass("d-flex"),t.removeClass("unloaded"),l.removeClass("unloaded"),e.removeClass("unloaded")}},f=function(){let t=!1;return{on(){t||(u.block(),r.removeClass("unloaded"),s.addClass("unloaded"),t=!0)},off(){t&&(i.empty(),c.hasClass("unloaded")&&c.removeClass("unloaded"),r.addClass("unloaded"),a.removeClass("visible"),s.removeClass("unloaded"),u.release(),d.val(""),t=!1)},isVisible(){return t}}}();function m(){return o.hasClass("loaded")}e.click(function(){p.on(),f.on(),d.focus()}),o.click(function(){p.off(),f.off()}),d.focus(function(){n.addClass("input-focus")}),d.focusout(function(){n.removeClass("input-focus")}),d.on("keyup",function(t){8===t.keyCode&&""===d.val()?m()?c.removeClass("unloaded"):f.off():""!==d.val()&&(f.on(),a.hasClass("visible")||a.addClass("visible"),m()&&c.addClass("unloaded"))}),a.on("click",function(){d.val(""),m()?(c.removeClass("unloaded"),i.empty()):f.off(),d.focus(),a.removeClass("visible")})}),$(function(){var t=function(){const t="sidebar-display";let e=!1;const o=$("body");return{toggle(){!1===e?o.attr(t,""):o.removeAttr(t),e=!e}}}();$("#sidebar-trigger").click(t.toggle),$("#mask").click(t.toggle)}),$(function(){$('[data-toggle="tooltip"]').tooltip()}),$(function(){const o=$("#topbar-wrapper"),e=$("#topbar-title"),a=$("#panel-wrapper"),s=$("#search-input"),l="topbar-up",n="topbar-down",r="toc-scrolling-up";let i,d=0;const c=o.outerHeight(),u=o.outerHeight();$(window).scroll(function(t){e.is(":hidden")&&(i=!0)}),setInterval(function(){i&&(function(){var t,e=$(this).scrollTop();Math.abs(d-e)<=c||(e>d?e>u&&(o.removeClass(n).addClass(l),a.removeClass(n),s.is(":focus")&&s.blur()):e+$(window).height()<$(document).height()&&(void 0!==(t=o.attr(r))?"false"===t&&o.removeAttr(r):(o.removeClass(l).addClass(n),a.addClass(n))),d=e)}(),i=!1)},250)}),$(function(){var e="div.post>h1:first-of-type";const o=$(e),n=$("#topbar-title");if(0!==o.length&&!o.hasClass("dynamic-title")&&!n.is(":hidden")){const r=n.text().trim();let a=o.text().trim(),s=!1,l=0;($("#page-category").length||$("#page-tag").length)&&/\s/.test(a)&&(a=a.replace(/[0-9]/g,"").trim());let t=new IntersectionObserver(t=>{var e,o;s?(e=$(window).scrollTop(),o=l<e,l=e,t=t[0],o?0===t.intersectionRatio&&n.text(a):1===t.intersectionRatio&&n.text(r)):s=!0},{rootMargin:"-48px 0px 0px 0px",threshold:[0,1]});t.observe(document.querySelector(e)),n.click(function(){$("body,html").animate({scrollTop:0},800)})}}),$(function(){let o=$(".timeago").length,t=void 0;const s=$("meta[name=day-prompt]").attr("content"),l=$("meta[name=hour-prompt]").attr("content"),n=$("meta[name=minute-prompt]").attr("content"),r=$("meta[name=justnow-prompt]").attr("content");function e(){return $(".timeago").each(function(){var t,e;!1!==$(this)[0].hasAttribute("date")?(e=function(t,e){let o=new Date,a=new Date(t);return a.getFullYear()!==o.getFullYear()||a.getMonth()!==o.getMonth()?e:(t=Math.floor((o-a)/1e3),1<=(e=Math.floor(t/86400))?` ${e} `+s:1<=(e=Math.floor(t/3600))?` ${e} `+l:1<=(t=Math.floor(t/60))?` ${t} `+n:r)}($(this).attr("date"),t=$(this).text()))===t?$(this).removeAttr("date"):$(this).text(e):--o}),0===o&&void 0!==t&&clearInterval(t),o}0!==o&&0<e()&&(t=setInterval(e,6e4))});
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diff --git a/assets/js/dist/page.min.js b/assets/js/dist/page.min.js
index a97ed22..e03b857 100644
--- a/assets/js/dist/page.min.js
+++ b/assets/js/dist/page.min.js
@@ -3,4 +3,4 @@
  * © 2019 Cotes Chung
  * MIT Licensed
  */
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diff --git a/assets/js/dist/post.min.js b/assets/js/dist/post.min.js
index fe9beb6..72887d9 100644
--- a/assets/js/dist/post.min.js
+++ b/assets/js/dist/post.min.js
@@ -3,4 +3,4 @@
  * © 2019 Cotes Chung
  * MIT Licensed
  */
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