From b5cd4f14923ac482b2fd4f8a8a63456b128303c6 Mon Sep 17 00:00:00 2001
From: Daniel Imms <2193314+Tyriar@users.noreply.github.com>
Date: Thu, 27 Oct 2022 16:50:45 -0700
Subject: [PATCH] Cache ICoreBrowserService.isFocused per task

This is called for every selected cell when rendering which ends up
consuming a bunch of CPU due to the DOM calls.
---
 src/browser/services/CoreBrowserService.ts | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/src/browser/services/CoreBrowserService.ts b/src/browser/services/CoreBrowserService.ts
index 6504e5e4..e992f255 100644
--- a/src/browser/services/CoreBrowserService.ts
+++ b/src/browser/services/CoreBrowserService.ts
@@ -8,10 +8,15 @@ import { ICoreBrowserService } from './Services';
 export class CoreBrowserService implements ICoreBrowserService {
   public serviceBrand: undefined;
 
+  private _isFocused = false;
+  private _cachedIsFocused: boolean | undefined = undefined;
+
   constructor(
     private _textarea: HTMLTextAreaElement,
     public readonly window: Window & typeof globalThis
   ) {
+    this._textarea.addEventListener('focus', () => this._isFocused = true);
+    this._textarea.addEventListener('blur', () => this._isFocused = false);
   }
 
   public get dpr(): number {
@@ -19,7 +24,10 @@ export class CoreBrowserService implements ICoreBrowserService {
   }
 
   public get isFocused(): boolean {
-    const docOrShadowRoot = this._textarea.getRootNode ? this._textarea.getRootNode() as Document | ShadowRoot : this._textarea.ownerDocument;
-    return docOrShadowRoot.activeElement === this._textarea && this._textarea.ownerDocument.hasFocus();
+    if (this._cachedIsFocused === undefined) {
+      this._cachedIsFocused = this._isFocused && this._textarea.ownerDocument.hasFocus();
+      queueMicrotask(() => this._cachedIsFocused = undefined);
+    }
+    return this._cachedIsFocused;
   }
 }