From cb9eec9f079949c99ac5f32bcd36b90dec07bd11 Mon Sep 17 00:00:00 2001
From: Ruben Bridgewater <ruben@bridgewater.de>
Date: Thu, 19 Nov 2020 16:36:01 +0100
Subject: [PATCH] util: fix instanceof checks with null prototypes during
 inspection

Signed-off-by: Ruben Bridgewater <ruben@bridgewater.de>

Fixes: https://github.com/nodejs/node/issues/35730
---
 lib/internal/util/inspect.js       | 10 +++++++++-
 test/parallel/test-util-inspect.js | 11 +++++++++++
 2 files changed, 20 insertions(+), 1 deletion(-)

diff --git a/lib/internal/util/inspect.js b/lib/internal/util/inspect.js
index e6bba524c07288..bd7a17166d0ed1 100644
--- a/lib/internal/util/inspect.js
+++ b/lib/internal/util/inspect.js
@@ -534,6 +534,14 @@ function getEmptyFormatArray() {
   return [];
 }
 
+function isInstanceof(object, proto) {
+  try {
+    return object instanceof proto;
+  } catch {
+    return false;
+  }
+}
+
 function getConstructorName(obj, ctx, recurseTimes, protoProps) {
   let firstProto;
   const tmp = obj;
@@ -542,7 +550,7 @@ function getConstructorName(obj, ctx, recurseTimes, protoProps) {
     if (descriptor !== undefined &&
         typeof descriptor.value === 'function' &&
         descriptor.value.name !== '' &&
-        tmp instanceof descriptor.value) {
+        isInstanceof(tmp, descriptor.value)) {
       if (protoProps !== undefined &&
          (firstProto !== obj ||
          !builtInObjects.has(descriptor.value.name))) {
diff --git a/test/parallel/test-util-inspect.js b/test/parallel/test-util-inspect.js
index 634f27690e5a59..56065beb458832 100644
--- a/test/parallel/test-util-inspect.js
+++ b/test/parallel/test-util-inspect.js
@@ -2866,6 +2866,17 @@ assert.strictEqual(
   );
 }
 
+// Check that prototypes with a null prototype are inspectable.
+// Regression test for https://github.com/nodejs/node/issues/35730
+{
+  function Func() {}
+  Func.prototype = null;
+  const object = {};
+  object.constructor = Func;
+
+  assert.strictEqual(util.inspect(object), '{ constructor: [Function: Func] }');
+}
+
 // Test changing util.inspect.colors colors and aliases.
 {
   const colors = util.inspect.colors;