Question

Try executing the following in JavaScript:

parseInt('01'); //equals 1
parseInt('02'); //equals 2
parseInt('03'); //equals 3
parseInt('04'); //equals 4
parseInt('05'); //equals 5
parseInt('06'); //equals 6
parseInt('07'); //equals 7
parseInt('08'); //equals 0 !!
parseInt('09'); //equals 0 !!

I just learned the hard way that JavaScript thinks the leading zero indicates an octal integer, and since there is no "8" or "9" in base-8, the function returns zero. Like it or not, this is by design.

What are the workarounds?

Note: For sake of completeness, I’m about to post a solution, but it’s a solution that I hate, so please post other/better answers.

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Update:

The 5th Edition of the JavaScript standard (ECMA-262) introduces a breaking change that eliminates this behavior. Mozilla has a good write-up.

Answer 1

This is a common Javascript gotcha with a simple solution:

Just specify the base, or ‘radix’, like so:

parseInt('08',10); // 8

You could also use Number:

Number('08'); // 8