Is the bug valid?

Yesterday we received a bug report that one of our text fields were defaulting to 00 when the user enters in 08 or 09.  Confused as to what could be causing this I fired up my various browsers and iOS simulator and was not able to duplicate the problem.

The Code

Looking at the code it was something like this:

   1: var num = $(this).val(), //val() would be "08" or "09"

   2:     theInt = parseInt(num);

Nothing seems out of the ordinary and everything is working correctly.  What could possibly be happening?  From there I started spinning up older versions of iOS5 and android.  Bam, the bug presents it self and is easily reproducible.

Debugging

Next up I wanted to figure out what the heck could be going on, so now the code morphed to the following.

   1: var num = $(this).val(),

   2:     theInt = parseInt(num);

   3:  

   4: alert(num); //alerts "08"

   5: alert(theInt); //alerts 0

Well it looks like we found our problem, parseInt() is some how behaving differently depending on the version of the browser, but why?

To the google!

After a few searches I soon smacked my head and said, darn it I forgot the radix!  The radix specifies which numeral system to use when parsing the number.  But why does it work correctly in new browsers but incorrectly in older ones?  Well after a bit more research I found this blurb on mozilla

ECMAScript 5 Removes Octal Interpretation

The ECMAScript 5 specification of the function parseInt no longer allows implementations to treat Strings beginning with a 0 character as octal values. ECMAScript 5 states:

The parseInt function produces an integer value dictated by interpretation of the contents of the string argument according to the specified radix. Leading white space in string is ignored. If radix is undefined or 0, it is assumed to be 10 except when the number begins with the character pairs 0x or 0X, in which case a radix of 16 is assumed. If radix is 16, number may also optionally begin with the character pairs 0x or 0X.

This differs from ECMAScript 3, which discouraged but allowed octal interpretation.

Since many implementations have not adopted this behavior as of 2011, and because older browsers must be supported, always specify a radix.

The key part is that in older browsers when no radix was specified the radix would default to 8, while in new browsers the radix is assumed to be 10.

The Fix

Well since we now know the problem we can easily fix the code to look something like this:

   1: var num = $(this).val(),

   2:     theInt = parseInt(num, 10);

Now the script works correctly on new and older browsers and we no longer have the undesired behavior we had previously.