From 1ce2211c984eb8c7913d384b443a088dafadf7ba Mon Sep 17 00:00:00 2001
From: "Michael[tm] Smith" <mike@w3.org>
Date: Mon, 15 Mar 2021 16:04:14 +0900
Subject: [PATCH] Recommend Number.isNaN(), not global isNan()

Fixes https://github.com/mdn/content/issues/3026
---
 .../index.html                                | 20 +++++++++++++++++--
 1 file changed, 18 insertions(+), 2 deletions(-)

diff --git a/files/en-us/web/javascript/a_re-introduction_to_javascript/index.html b/files/en-us/web/javascript/a_re-introduction_to_javascript/index.html
index eea024dca7c6f1a..e2fa5b31c137456 100644
--- a/files/en-us/web/javascript/a_re-introduction_to_javascript/index.html
+++ b/files/en-us/web/javascript/a_re-introduction_to_javascript/index.html
@@ -119,9 +119,25 @@ <h2 id="Numbers">Numbers</h2>
 <pre class="brush: js">NaN + 5; // NaN
 </pre>
 
-<p>You can test for <code>NaN</code> using the built-in {{jsxref("Global_Objects/isNaN", "isNaN()")}} function:</p>
+<p>You can reliably test for <code>NaN</code> using the built-in {{jsxref("Number.isNaN", "Number.isNaN()")}} function:</p>
 
-<pre class="brush: js">isNaN(NaN); // true
+<pre class="brush: js">Number.isNaN(NaN); // true
+Number.isNaN('hello'); // false
+Number.isNaN('1'); // false
+Number.isNaN(undefined); // false
+Number.isNaN({}); // false
+Number.isNaN([1]) // false
+Number.isNaN([1,2]) // false
+</pre>
+
+<p>But don’t test for <code>NaN</code> using the global {{jsxref("Global_Objects/isNaN", "isNaN()")}} function, which has unintuitive behavior:</p>
+
+<pre class="brush: js">isNaN('hello'); // true
+isNaN('1'); // false
+isNaN(undefined); // true
+isNaN({}); // true
+isNaN([1]) // false
+isNaN([1,2]) // true
 </pre>
 
 <p>JavaScript also has the special values {{jsxref("Infinity")}} and <code>-Infinity</code>:</p>