From 909ff8e29fa653be95ec36430971fe4b9d3394e4 Mon Sep 17 00:00:00 2001
From: Jonas Jenwald <jonas.jenwald@gmail.com>
Date: Sat, 3 Jul 2021 11:15:13 +0200
Subject: [PATCH] Replace `instanceof Object` with `typeof` checks

Using `instanceof Object` is generally problematic, since it's not guaranteed to always do the right thing for all Objects.
(I stumbled upon this while working on another patch, when I noticed that the `outlineView` was broken with workers disabled.)
---
 .eslintrc                  | 4 ++++
 src/core/xfa/xfa_object.js | 2 +-
 web/pdf_link_service.js    | 2 +-
 web/pdf_outline_viewer.js  | 2 +-
 4 files changed, 7 insertions(+), 3 deletions(-)

diff --git a/.eslintrc b/.eslintrc
index 1692ccf16..982f9e4af 100644
--- a/.eslintrc
+++ b/.eslintrc
@@ -166,6 +166,10 @@
     "no-nested-ternary": "error",
     "no-new-object": "error",
     "no-restricted-syntax": ["error",
+      {
+        "selector": "BinaryExpression[operator='instanceof'][right.name='Object']",
+        "message": "Use `typeof` rather than `instanceof Object`.",
+      },
       {
         "selector": "CallExpression[callee.name='assert'][arguments.length!=2]",
         "message": "`assert()` must always be invoked with two arguments.",
diff --git a/src/core/xfa/xfa_object.js b/src/core/xfa/xfa_object.js
index a890bcc05..d8fbaa09a 100644
--- a/src/core/xfa/xfa_object.js
+++ b/src/core/xfa/xfa_object.js
@@ -586,7 +586,7 @@ class XFAObject {
     if (Array.isArray(obj)) {
       return obj.map(x => XFAObject[_cloneAttribute](x));
     }
-    if (obj instanceof Object) {
+    if (typeof obj === "object" && obj !== null) {
       return Object.assign({}, obj);
     }
     return obj;
diff --git a/web/pdf_link_service.js b/web/pdf_link_service.js
index 54ff04594..e73c11fe1 100644
--- a/web/pdf_link_service.js
+++ b/web/pdf_link_service.js
@@ -114,7 +114,7 @@ class PDFLinkService {
     const destRef = explicitDest[0];
     let pageNumber;
 
-    if (destRef instanceof Object) {
+    if (typeof destRef === "object" && destRef !== null) {
       pageNumber = this._cachedPageNumber(destRef);
 
       if (pageNumber === null) {
diff --git a/web/pdf_outline_viewer.js b/web/pdf_outline_viewer.js
index 1017fe737..00cabc81d 100644
--- a/web/pdf_outline_viewer.js
+++ b/web/pdf_outline_viewer.js
@@ -304,7 +304,7 @@ class PDFOutlineViewer extends BaseTreeViewer {
         if (Array.isArray(explicitDest)) {
           const [destRef] = explicitDest;
 
-          if (destRef instanceof Object) {
+          if (typeof destRef === "object" && destRef !== null) {
             pageNumber = this.linkService._cachedPageNumber(destRef);
 
             if (!pageNumber) {