From 36a096c9b60bd6b3b086f2c966a1cd40dbc54473 Mon Sep 17 00:00:00 2001
From: Amanda Smith <90629384+amandaesmith3@users.noreply.github.com>
Date: Wed, 24 Nov 2021 08:40:36 -0600
Subject: [PATCH] fix(content): ensure scrollEl is always available in scroll
 methods (#24255)

---
 core/src/components/content/content.tsx | 29 +++++++++++++++++--------
 1 file changed, 20 insertions(+), 9 deletions(-)

diff --git a/core/src/components/content/content.tsx b/core/src/components/content/content.tsx
index 290bd4c447..7696b0d692 100644
--- a/core/src/components/content/content.tsx
+++ b/core/src/components/content/content.tsx
@@ -2,6 +2,7 @@ import { Component, ComponentInterface, Element, Event, EventEmitter, Host, List
 
 import { getIonMode } from '../../global/ionic-global';
 import { Color, ScrollBaseDetail, ScrollDetail } from '../../interface';
+import { componentOnReady } from '../../utils/helpers';
 import { isPlatform } from '../../utils/platform';
 import { createColorClasses, hostContext } from '../../utils/theme';
 
@@ -25,7 +26,7 @@ export class Content implements ComponentInterface {
   private queued = false;
   private cTop = -1;
   private cBottom = -1;
-  private scrollEl!: HTMLElement;
+  private scrollEl?: HTMLElement;
   private isMainContent = true;
 
   // Detail is used in a hot loop in the scroll event, by allocating it here
@@ -168,7 +169,7 @@ export class Content implements ComponentInterface {
       readTask(ts => {
         this.queued = false;
         this.detail.event = ev;
-        updateScrollDetail(this.detail, this.scrollEl, ts, shouldStart);
+        updateScrollDetail(this.detail, this.scrollEl!, ts, shouldStart);
         this.ionScroll.emit(this.detail);
       });
     }
@@ -183,8 +184,16 @@ export class Content implements ComponentInterface {
    * and `scrollToPoint()` to scroll the content into a certain point.
    */
   @Method()
-  getScrollElement(): Promise<HTMLElement> {
-    return Promise.resolve(this.scrollEl);
+  async getScrollElement(): Promise<HTMLElement> {
+    /**
+     * If this gets called in certain early lifecycle hooks (ex: Vue onMounted),
+     * scrollEl won't be defined yet with the custom elements build, so wait for it to load in.
+     */
+    if (!this.scrollEl) {
+      await new Promise(resolve => componentOnReady(this.el, resolve));
+    }
+
+    return Promise.resolve(this.scrollEl!);
   }
 
   /**
@@ -203,8 +212,9 @@ export class Content implements ComponentInterface {
    * @param duration The amount of time to take scrolling to the bottom. Defaults to `0`.
    */
   @Method()
-  scrollToBottom(duration = 0): Promise<void> {
-    const y = this.scrollEl.scrollHeight - this.scrollEl.clientHeight;
+  async scrollToBottom(duration = 0): Promise<void> {
+    const scrollEl = await this.getScrollElement();
+    const y = scrollEl!.scrollHeight - scrollEl!.clientHeight;
     return this.scrollToPoint(undefined, y, duration);
   }
 
@@ -216,8 +226,9 @@ export class Content implements ComponentInterface {
    * @param duration The amount of time to take scrolling by that amount.
    */
   @Method()
-  scrollByPoint(x: number, y: number, duration: number): Promise<void> {
-    return this.scrollToPoint(x + this.scrollEl.scrollLeft, y + this.scrollEl.scrollTop, duration);
+  async scrollByPoint(x: number, y: number, duration: number): Promise<void> {
+    const scrollEl = await this.getScrollElement();
+    return this.scrollToPoint(x + scrollEl!.scrollLeft, y + scrollEl!.scrollTop, duration);
   }
 
   /**
@@ -229,7 +240,7 @@ export class Content implements ComponentInterface {
    */
   @Method()
   async scrollToPoint(x: number | undefined | null, y: number | undefined | null, duration = 0): Promise<void> {
-    const el = this.scrollEl;
+    const el = await this.getScrollElement();
     if (duration < 32) {
       if (y != null) {
         el.scrollTop = y;