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Recommend Number.isNaN(), not global isNan() #3135

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Mar 16, 2021
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Recommend Number.isNaN(), not global isNan() #3135

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Recommend Number.isNaN(), not global isNan()
sideshowbarker Mar 15, 2021
84e4d21
Add links to more-detailed explanations
sideshowbarker Mar 16, 2021
1881ebf
Apply suggestions from code review
sideshowbarker Mar 16, 2021
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20 changes: 18 additions & 2 deletions files/en-us/web/javascript/a_re-introduction_to_javascript/index.html
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Expand Up @@ -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, <a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/Number/isNaN#description">which behaves just as its name implies</a>:</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, <a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/isNaN#confusing_special-case_behavior">which has unintuitive behavior</a>:</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>
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