Revision 1065392 of SyntaxError: "x" is not a legal ECMA-262 octal constant

<div>{{jsSidebar("Errors")}}</div>

<h2 id="Message">Message</h2>

<pre class="syntaxbox">
Warning: SyntaxError: 08 is not a legal ECMA-262 octal constant.
Warning: SyntaxError: 09 is not a legal ECMA-262 octal constant.
</pre>

<h2 id="Error_type">Error type</h2>

<p>{{jsxref("SyntaxError")}} warning in <a href="/en-US/docs/Web/JavaScript/Reference/Strict_mode">strict mode</a> only.</p>

<h2 id="What_went_wrong">What went wrong?</h2>

<p>Decimal literals can start with a zero (<code>0</code>) followed by another decimal digit, but If all digits after the leading <code>0</code> are smaller than 8, the number is interpreted as an octal number. Because this is not the case with <code>08</code> and <code>09</code>, JavaScript warns about it.</p>

<p>Note that octal literals and octal escape sequences are deprecated and will present an additional deprecation warning. With ECMAScript 6 and later, the syntax uses a leading zero followed by a lowercase or uppercase Latin letter "O" (<code>0o</code> or <code>0O)</code>. See the page about <a href="/en-US/docs/Web/JavaScript/Reference/Lexical_grammar#Octal">lexical grammar</a> for more information.</p>

<h2 id="Examples">Examples</h2>

<h3>Invalid octal numbers</h3>

<pre class="brush: js example-bad">
08;
09;
// SyntaxError: 08 is not a legal ECMA-262 octal constant
// SyntaxError: octal literals and octal escape sequences are deprecated</pre>

<h3>Valid octal numbers</h3>

<p>Use a leading zero followed by the letter "o";</p>

<pre class="brush: js example-good">
0O755;
0o644;
</pre>

<h2 id="See_also">See also</h2>

<ul>
 <li><a href="/en-US/docs/Web/JavaScript/Reference/Lexical_grammar#Octal">Lexical grammar</a></li>
</ul>