From a82aeeaa5e06cf7cccc5e2d5da468c26c8e57797 Mon Sep 17 00:00:00 2001
From: Sindre Sorhus <sindresorhus@gmail.com>
Date: Sun, 31 Oct 2021 12:34:45 +0700
Subject: [PATCH] Add FAQ about `instanceof`

---
 readme.md | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/readme.md b/readme.md
index c9b5463..f956fcc 100644
--- a/readme.md
+++ b/readme.md
@@ -602,6 +602,10 @@ For the ones I found, pick 3 of these.
 
 The most common mistakes I noticed in these modules was using `instanceof` for type checking, forgetting that functions are objects, and omitting `symbol` as a primitive.
 
+### Why not just use `instanceof` instead of this package?
+
+`instanceof` does not work correctly for all types and it does not work across [realms](https://stackoverflow.com/a/49832343/64949). Examples of realms are iframes, windows, web workers, and the `vm` module in Node.js.
+
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