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copied!<p>Mozilla <a href="https://developer.mozilla.org/en/JavaScript/Reference/Global_Objects/parseInt">tells us</a>:</p> <blockquote> <p>function parseInt <strong>converts its first argument to a string</strong>, parses it, and returns an integer or NaN. If not NaN, the returned value will be the decimal integer representation of the first argument taken as a number in the specified radix (base). For example, a radix of 10 indicates to convert from a decimal number, 8 octal, 16 hexadecimal, and so on. For radices above 10, the letters of the alphabet indicate numerals greater than 9. For example, for hexadecimal numbers (base 16), A through F are used.</p> </blockquote> <p>In <a href="http://www.ecma-international.org/publications/files/ECMA-ST/ECMA-262.pdf">the spec</a>, 15.1.2.2/1 tells us that the conversion to string is performed using the built-in <code>ToString</code>, which (as per 9.8) yields <code>"null"</code> (not to be confused with <code>toString</code>, which would yield <code>"[object Window]"</code>!).</p> <p>So, let's consider <code>parseInt("null", 24)</code>.</p> <p>Of course, this isn't a base-24 numeric string in entirety, but "n" is: it's <em>decimal 23</em>. </p> <p>Now, parsing stops after the decimal 23 is pulled out, because <code>"u"</code> <em>isn't</em> found in the base-24 system:</p> <blockquote> <p>If S contains any character that is not a radix-R digit, then let Z be the substring of S consisting of all characters before the first such character; otherwise, let Z be S. [15.1.2.2/11]</p> </blockquote> <p>(And this is why <code>parseInt(null, 23)</code> (and lower radices) gives you <code>NaN</code> rather than 23: <code>"n"</code> is not in the base-23 system.)</p>

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