From b36f21cbaff7c885223b44267c70e6711b754af6 Mon Sep 17 00:00:00 2001
From: Tim Dorr <timdorr@users.noreply.github.com>
Date: Wed, 8 Nov 2017 14:11:20 -0500
Subject: [PATCH] Faster/simpler isPlainObject check (#3483)

Faster/simpler isPlainObject check.

This runs up the prototype chain to check equivalency. When run in a cross-realm environment (differing contexts, iframes, etc), this ensures we're checking the value's prototype matches its context-specific instance of Object.

This is faster than calling `toString()` on the constructor. There's still the `baseGetTag()` call, which does its own `toString()`, but this swaps out one for cross-realm stuff. It's also a bit simpler to understand, I think.
---
 isPlainObject.js | 20 ++++++--------------
 1 file changed, 6 insertions(+), 14 deletions(-)

diff --git a/isPlainObject.js b/isPlainObject.js
index beba9ec21..34dcf9af8 100644
--- a/isPlainObject.js
+++ b/isPlainObject.js
@@ -1,15 +1,6 @@
 import baseGetTag from './.internal/baseGetTag.js'
 import isObjectLike from './isObjectLike.js'
 
-/** Used to resolve the decompiled source of functions. */
-const funcToString = Function.prototype.toString
-
-/** Used to check objects for own properties. */
-const hasOwnProperty = Object.prototype.hasOwnProperty
-
-/** Used to infer the `Object` constructor. */
-const objectCtorString = funcToString.call(Object)
-
 /**
  * Checks if `value` is a plain object, that is, an object created by the
  * `Object` constructor or one with a `[[Prototype]]` of `null`.
@@ -40,13 +31,14 @@ function isPlainObject(value) {
   if (!isObjectLike(value) || baseGetTag(value) != '[object Object]') {
     return false
   }
-  const proto = Object.getPrototypeOf(value)
-  if (proto === null) {
+  if (Object.getPrototypeOf(value) === null) {
     return true
   }
-  const Ctor = hasOwnProperty.call(proto, 'constructor') && proto.constructor
-  return typeof Ctor == 'function' && Ctor instanceof Ctor &&
-    funcToString.call(Ctor) == objectCtorString
+  let proto = value
+  while (Object.getPrototypeOf(proto) !== null) {
+    proto = Object.getPrototypeOf(proto)
+  }
+  return Object.getPrototypeOf(value) === proto
 }
 
 export default isPlainObject