From 90ee1fab375fccfd9b926df718243339b4976d50 Mon Sep 17 00:00:00 2001
From: doowb <brian.woodward@gmail.com>
Date: Mon, 24 Jun 2019 16:31:42 -0400
Subject: [PATCH] ensure keys are valid when mixing in values

---
 index.js | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/index.js b/index.js
index 909fbef..47face2 100644
--- a/index.js
+++ b/index.js
@@ -23,7 +23,7 @@ function mixinDeep(target, objects) {
  */
 
 function copy(val, key) {
-  if (key === '__proto__') {
+  if (!isValidKey(key)) {
     return;
   }
 
@@ -46,6 +46,17 @@ function isObject(val) {
   return isExtendable(val) && !Array.isArray(val);
 }
 
+/**
+ * Returns true if `key` is a valid key to use when extending objects.
+ *
+ * @param  {String} `key`
+ * @return {Boolean}
+ */
+
+function isValidKey(key) {
+  return key !== '__proto__' && key !== 'constructor' && key !== 'prototype';
+};
+
 /**
  * Expose `mixinDeep`
  */