feat: Change the highlight in article page on scrolling (#8330)

app/javascript/portal/components/TableOfContents.vue

@@ -2,27 +2,21 @@
   <div class="hidden lg:block flex-1 py-6 scroll-mt-24 pl-4">
     <div v-if="rows.length > 0" class="sticky top-24 py-2 overflow-auto">
       <nav class="max-w-2xl">
-        <h2
-          id="on-this-page-title"
-          class="text-slate-800 pl-6 dark:text-slate-50 font-semibold tracking-wide py-3 leading-7 border-l-2 border-solid border-slate-100 dark:border-slate-800"
-          :class="{
-            '!border-slate-400 dark:!border-slate-100': !currentSlug,
-          }"
+        <ol
+          role="list"
+          class="flex flex-col gap-2 text-base border-l-2 border-solid border-slate-100 dark:border-slate-800"
         >
-          {{ tocHeader }}
-        </h2>
-        <ol role="list" class="text-base">
           <li
             v-for="element in rows"
             :key="element.slug"
-            class="leading-6 py-2 pl-6 border-l-2 border-solid"
+            class="leading-6 border-l-2 relative -left-0.5 border-solid"
             :class="elementBorderStyles(element)"
           >
-            <p :class="getClassName(element)">
+            <p class="py-2 px-4" :class="getClassName(element)">
               <a
                 :href="`#${element.slug}`"
                 data-turbolinks="false"
-                class="text-base cursor-pointer"
+                class="font-medium text-sm tracking-[0.28px] cursor-pointer"
                 :class="elementTextStyles(element)"
               >
                 {{ element.title }}
@@ -45,12 +39,10 @@ export default {
   data() {
     return {
       currentSlug: window.location?.hash?.substring(1) || '',
+      intersectionObserver: null,
     };
   },
   computed: {
-    tocHeader() {
-      return window.portalConfig.tocHeader;
-    },
     h1Count() {
       return this.rows.filter(el => el.tag === 'h1').length;
     },
@@ -59,10 +51,14 @@ export default {
     },
   },
   mounted() {
+    this.initializeIntersectionObserver();
     window.addEventListener('hashchange', this.onURLHashChange);
   },
   beforeDestroy() {
     window.removeEventListener('hashchange', this.onURLHashChange);
+    if (this.intersectionObserver) {
+      this.intersectionObserver.disconnect();
+    }
   },
   methods: {
     getClassName(el) {
@@ -85,18 +81,32 @@ export default {
 
       return '';
     },
+    initializeIntersectionObserver() {
+      this.intersectionObserver = new IntersectionObserver(
+        entries => {
+          const currentSection = entries.find(entry => entry.isIntersecting);
+          if (currentSection) {
+            this.currentSlug = currentSection.target.id;
+          }
+        },
+        {
+          threshold: 0.25,
+          rootMargin: '0px 0px -20% 0px',
+        }
+      );
+
+      this.rows.forEach(el => {
+        const sectionElement = document.getElementById(el.slug);
+        if (!sectionElement) return;
+        this.intersectionObserver.observe(sectionElement);
+      });
+    },
     onURLHashChange() {
       this.currentSlug = window.location?.hash?.substring(1) || '';
     },
     isElementActive(el) {
       return this.currentSlug === el.slug;
     },
-    tocHeaderBorderStyles() {
-      if (this.currentSlug === '') {
-        return 'border-slate-400 dark:border-slate-100';
-      }
-      return 'border-slate-100 dark:border-slate-800';
-    },
     elementBorderStyles(el) {
       if (this.isElementActive(el)) {
         return 'border-slate-400 dark:border-slate-50 transition-colors duration-200';
@@ -105,7 +115,7 @@ export default {
     },
     elementTextStyles(el) {
       if (this.isElementActive(el)) {
-        return 'font-semibold text-slate-900 dark:text-slate-25';
+        return 'text-slate-900 dark:text-slate-25 transition-colors duration-200';
       }
       return 'text-slate-700 dark:text-slate-100';
     },