fix scrolling for markdown content, which is loaded asynchronous

The code to find and scroll to the anchor is now moved from the
ScrollToTop component to the MarkdownView. The anchor with the id from
location hash, is searched after the MarkdownView and all its children
finished rendering.

scm-ui-components/packages/ui-components/src/MarkdownView.js

@@ -4,12 +4,17 @@ import SyntaxHighlighter from "./SyntaxHighlighter";
 import Markdown from "react-markdown/with-html";
 import {binder} from "@scm-manager/ui-extensions";
 import MarkdownHeadingRenderer from "./MarkdownHeadingRenderer";
+import { withRouter } from "react-router-dom";
+
 
 type Props = {
   content: string,
   renderContext?: Object,
   renderers?: Object,
-  enableAnchorHeadings: boolean
+  enableAnchorHeadings: boolean,
+
+  // context props
+  location: any
 };
 
 class MarkdownView extends React.Component<Props> {
@@ -18,10 +23,27 @@ class MarkdownView extends React.Component<Props> {
     enableAnchorHeadings: false
   };
 
+  contentRef: ?HTMLDivElement;
+
   constructor(props: Props) {
     super(props);
   }
 
+  componentDidUpdate() {
+    // we have to use componentDidUpdate, because we have to wait until all
+    // children are rendered and componentDidMount is called before the
+    // markdown content was rendered.
+    const hash = this.props.location.hash;
+    if (this.contentRef && hash) {
+      // we query only child elements, to avoid strange scrolling with multiple
+      // markdown elements on one page.
+      const element = this.contentRef.querySelector(hash);
+      if (element && element.scrollIntoView) {
+        element.scrollIntoView();
+      }
+    }
+  }
+
   render() {
     const {content, renderers, renderContext, enableAnchorHeadings} = this.props;
 
@@ -45,15 +67,17 @@ class MarkdownView extends React.Component<Props> {
     }
 
     return (
-      <Markdown
-        className="content"
-        skipHtml={true}
-        escapeHtml={true}
-        source={content}
-        renderers={rendererList}
-      />
+      <div ref={el => (this.contentRef = el)}>
+        <Markdown
+          className="content"
+          skipHtml={true}
+          escapeHtml={true}
+          source={content}
+          renderers={rendererList}
+        />
+      </div>
     );
   }
 }
 
-export default MarkdownView;
+export default withRouter(MarkdownView);

scm-ui/src/containers/ScrollToTop.js

@@ -11,15 +11,7 @@ type Props = {
 class ScrollToTop extends React.Component<Props> {
   componentDidUpdate(prevProps) {
     if (this.props.location.pathname !== prevProps.location.pathname) {
-      const hash = this.props.location.hash;
-      if (hash) {
-        const element = document.getElementById(hash.substring(1));
-        if (element && element.scrollIntoView) {
-          element.scrollIntoView();
-        }
-      } else {
-        window.scrollTo(0, 0);
-      }
+      window.scrollTo(0, 0);
     }
   }