Update src/app/components/table-of-content/table-of-content.component.ts

Co-authored-by: Robinson Zimmermann <[email protected]>

src/app/components/table-of-content/table-of-content.component.ts

@@ -31,7 +31,7 @@ export class TableOfContentComponent implements AfterViewInit {
     this.dataSource.data = headers;
     this.treeControl.expandAll();
     if (headers.length) {
-      this.createOffsets(headers);
+      this.offsetHeaders = this.createOffsets(headers);
       this.checkFirstHeader();
     }
   }
@@ -50,20 +50,30 @@ export class TableOfContentComponent implements AfterViewInit {
       const fullHeight =
         this.document.body.scrollHeight - this.document.body.clientHeight;
 
+      if (scroll === fullHeight) {
+        this.activeHeader = this.offsetHeaders[this.offsetHeaders.length - 1];
+        return;
+      }
+
+      const firstElementOffset = this.document.getElementById(this.offsetHeaders[0])?.offsetTop;
+
+      if (scroll < Number(firstElementOffset)) {
+        this.activeHeader = this.offsetHeaders[0]
+        return
+      }
+
       this.activeHeader = this.offsetHeaders.find((element, i, offsetHeaders) => {
+
         const nextElement = offsetHeaders[i + 1];
 
         const offset = this.document.getElementById(element)?.offsetTop;
         const nextOffset = nextElement
           ? this.document.getElementById(nextElement)?.offsetTop
           : fullHeightWithScroll;
 
-        if (fullHeight === scroll && i === offsetHeaders.length) {
-          return true;
-        }
-
         return scroll >= Number(offset) && scroll < Number(nextOffset);
       });
+
     }
   }