From 7216511fbf16188bfa0a4fa13f7b217aec519656 Mon Sep 17 00:00:00 2001
From: Jonas Jenwald <jonas.jenwald@gmail.com>
Date: Sun, 17 Oct 2021 13:42:21 +0200
Subject: [PATCH] Convert `TempImageFactory` to a `class`, using static
 fields/methods

Please refer to https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Classes/Private_class_fields
---
 web/pdf_thumbnail_view.js | 70 ++++++++++++++++++---------------------
 1 file changed, 32 insertions(+), 38 deletions(-)

diff --git a/web/pdf_thumbnail_view.js b/web/pdf_thumbnail_view.js
index 4b43d26f1..0df790e90 100644
--- a/web/pdf_thumbnail_view.js
+++ b/web/pdf_thumbnail_view.js
@@ -36,48 +36,42 @@ const THUMBNAIL_WIDTH = 98; // px
  * @property {IL10n} l10n - Localization service.
  */
 
-const TempImageFactory = (function TempImageFactoryClosure() {
-  let tempCanvasCache = null;
+class TempImageFactory {
+  static #tempCanvas = null;
 
-  return {
-    getCanvas(width, height) {
-      let tempCanvas = tempCanvasCache;
-      if (!tempCanvas) {
-        tempCanvas = document.createElement("canvas");
-        tempCanvasCache = tempCanvas;
-      }
-      tempCanvas.width = width;
-      tempCanvas.height = height;
+  static getCanvas(width, height) {
+    const tempCanvas = (this.#tempCanvas ||= document.createElement("canvas"));
+    tempCanvas.width = width;
+    tempCanvas.height = height;
 
-      // Since this is a temporary canvas, we need to fill it with a white
-      // background ourselves. `_getPageDrawContext` uses CSS rules for this.
-      if (
-        typeof PDFJSDev === "undefined" ||
-        PDFJSDev.test("MOZCENTRAL || GENERIC")
-      ) {
-        tempCanvas.mozOpaque = true;
-      }
+    // Since this is a temporary canvas, we need to fill it with a white
+    // background ourselves. `_getPageDrawContext` uses CSS rules for this.
+    if (
+      typeof PDFJSDev === "undefined" ||
+      PDFJSDev.test("MOZCENTRAL || GENERIC")
+    ) {
+      tempCanvas.mozOpaque = true;
+    }
 
-      const ctx = tempCanvas.getContext("2d", { alpha: false });
-      ctx.save();
-      ctx.fillStyle = "rgb(255, 255, 255)";
-      ctx.fillRect(0, 0, width, height);
-      ctx.restore();
-      return [tempCanvas, tempCanvas.getContext("2d")];
-    },
+    const ctx = tempCanvas.getContext("2d", { alpha: false });
+    ctx.save();
+    ctx.fillStyle = "rgb(255, 255, 255)";
+    ctx.fillRect(0, 0, width, height);
+    ctx.restore();
+    return [tempCanvas, tempCanvas.getContext("2d")];
+  }
 
-    destroyCanvas() {
-      const tempCanvas = tempCanvasCache;
-      if (tempCanvas) {
-        // Zeroing the width and height causes Firefox to release graphics
-        // resources immediately, which can greatly reduce memory consumption.
-        tempCanvas.width = 0;
-        tempCanvas.height = 0;
-      }
-      tempCanvasCache = null;
-    },
-  };
-})();
+  static destroyCanvas() {
+    const tempCanvas = this.#tempCanvas;
+    if (tempCanvas) {
+      // Zeroing the width and height causes Firefox to release graphics
+      // resources immediately, which can greatly reduce memory consumption.
+      tempCanvas.width = 0;
+      tempCanvas.height = 0;
+    }
+    this.#tempCanvas = null;
+  }
+}
 
 /**
  * @implements {IRenderableView}