From c594dff9413a18615be661edb271b343aeeb69a0 Mon Sep 17 00:00:00 2001
From: Sarah Edwards <skedwards88@github.com>
Date: Tue, 15 Jun 2021 15:44:02 -0700
Subject: [PATCH] fix ts bug (#19945)

---
 javascripts/display-tool-specific-content.ts | 8 ++++++--
 javascripts/scroll-anchoring.d.ts            | 5 +++++
 2 files changed, 11 insertions(+), 2 deletions(-)
 create mode 100644 javascripts/scroll-anchoring.d.ts

diff --git a/javascripts/display-tool-specific-content.ts b/javascripts/display-tool-specific-content.ts
index 7f69193dd5..92c8fb1a2e 100644
--- a/javascripts/display-tool-specific-content.ts
+++ b/javascripts/display-tool-specific-content.ts
@@ -1,4 +1,5 @@
 import Cookies from 'js-cookie'
+import { preserveAnchorNodePosition } from 'scroll-anchoring'
 
 import { sendEvent, EventType } from './events'
 
@@ -29,7 +30,9 @@ export default function displayToolSpecificContent() {
       event.preventDefault()
       const target = event.target as HTMLElement
       highlightTabForTool(target.dataset.tool || '')
-      showToolSpecificContent(target.dataset.tool || '', toolElements)
+      preserveAnchorNodePosition(document, () => {
+        showToolSpecificContent(target.dataset.tool || '', toolElements)
+      })
 
       // Save this preference as a cookie.
       Cookies.set('toolPreferred', target.dataset.tool || '', { sameSite: 'strict', secure: true })
@@ -76,7 +79,8 @@ function getDefaultTool(detectedTools: Array<string>): string {
 
   // If there is a default tool and the tool is present on this page
   const defaultToolEl = document.querySelector('[data-default-tool]') as HTMLElement
-  const defaultToolValue = defaultToolEl.dataset.defaultTool
+
+  const defaultToolValue = defaultToolEl ? defaultToolEl.dataset.defaultTool : ''
   if (defaultToolValue && detectedTools.includes(defaultToolValue)) {
     return defaultToolValue
   }
diff --git a/javascripts/scroll-anchoring.d.ts b/javascripts/scroll-anchoring.d.ts
new file mode 100644
index 0000000000..8ec46667fe
--- /dev/null
+++ b/javascripts/scroll-anchoring.d.ts
@@ -0,0 +1,5 @@
+declare module 'scroll-anchoring' {
+  export function findAnchorNode(document: Document): Node | undefined
+  export function preserveAnchorNodePosition<T>(document: Document, callback: () => Promise<T> | T): Promise<T>
+  export function preservePosition<T>(anchorNode: Node, callback: () => Promise<T> | T): Promise<T>  
+}