why does console.log(0123); log 83?

Question

Why does console.log(0123); log the integer . 83? I'm not sure why it would and don't really have an idea either.

Possible duplicate of [Why does JavaScript output 16384 instead of 040000?](http://stackoverflow.com/questions/21036122/why-does-javascript-output-16384-instead-of-040000) — default locale, Oct 11 '16 at 06:30
Possible duplicate of [Prefix zero changes output in number addition](http://stackoverflow.com/questions/9139648/prefix-zero-changes-output-in-number-addition) — cske, Oct 11 '16 at 06:47

Robby Cornelissen · Accepted Answer · 2016-10-11T04:50:11.110

4

Because it's interpreted as an octal number, and octal 123 corresponds to decimal 83 (64 + 16 + 3).

From MDN:

Leading 0 (zero) on an integer literal, or leading 0o (or 0O) indicates it is in octal. Octal integers can include only the digits 0-7.

edited Oct 11 '16 at 04:50

answered Oct 11 '16 at 04:43

Robby Cornelissen

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Only when there is a 0 in front or for every integer? – Alexander John Oct 11 '16 at 04:44
Only when there's a `0`, `0o` or `0O` in front. – Robby Cornelissen Oct 11 '16 at 04:59
Note that in strict mode you'll get `SyntaxError: Octal literals are not allowed in strict mode.` for the literal `0123` but *not* for `0o123`. – nnnnnn Oct 11 '16 at 05:19

score 0 · Answer 2 · answered Feb 25 '18 at 17:06

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Because the leading 0 (zero) 0o or 0O on an integer indicates an octal number!!

Octal numbering system is used less nowadays and has almost disappeared as a digital base number system. Hexadecimal numbering system is so popular now!

answered Feb 25 '18 at 17:06

Faisal Ahmed

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why does console.log(0123); log 83?

2 Answers2