fix: handle scrollYOffset in ScrollService

Author: RomanHotsiy

src/services/AppStore.ts

@@ -36,7 +36,7 @@ export class AppStore {
   constructor(spec: OpenAPISpec, specUrl?: string, options: RedocRawOptions = {}) {
     this.rawOptions = options;
     this.options = new RedocNormalizedOptions(options);
-    this.scroll = new ScrollService();
+    this.scroll = new ScrollService(this.options);
     this.spec = new SpecStore(spec, specUrl, this.options);
     this.menu = new MenuStore(this.spec, this.scroll);
   }

src/services/ScrollService.ts

@@ -2,14 +2,15 @@ import { debounce, bind } from 'decko';
 import { EventEmitter } from 'eventemitter3';
 
 import { querySelector, isBrowser } from '../utils';
+import { RedocNormalizedOptions } from './RedocNormalizedOptions';
 
 const EVENT = 'scroll';
 
 export class ScrollService {
   private _scrollParent: Window | HTMLElement | undefined;
   private _emiter: EventEmitter;
   private _prevOffsetY: number = 0;
-  constructor() {
+  constructor(private options: RedocNormalizedOptions) {
     this._scrollParent = isBrowser ? window : undefined;
     this._emiter = new EventEmitter();
     this.bind();
@@ -37,12 +38,12 @@ export class ScrollService {
 
   isElementBellow(el: Element | null) {
     if (el === null) return;
-    return el.getBoundingClientRect().top > 0;
+    return el.getBoundingClientRect().top > this.options.scrollYOffset();
   }
 
   isElementAbove(el: Element | null) {
     if (el === null) return;
-    return Math.trunc(el.getBoundingClientRect().top) <= 0;
+    return Math.trunc(el.getBoundingClientRect().top) <= this.options.scrollYOffset();
   }
 
   subscribe(cb): () => void {
@@ -55,6 +56,9 @@ export class ScrollService {
       return;
     }
     element.scrollIntoView();
+    this._scrollParent &&
+      this._scrollParent.scrollBy &&
+      this._scrollParent.scrollBy({ top: -this.options.scrollYOffset() });
   }
 
   scrollIntoViewBySelector(selector: string) {