We're not talking about parsing in base 10, we're talking about parsing in base 8. I need to be able to tell if the parse succeeded or not, silently hiding errors is bad. The correct behaviour demonstrated in perl and python:

    $ perl -le 'print 07'
    7
    $ perl -le 'print 08'
    Illegal octal digit '8' at -e line 1, at end of line
    Execution of -e aborted due to compilation errors.
    $ python -c 'print 07'
    7
    $ python -c 'print 08'
      File "", line 1
        print 08
       	^
    SyntaxError: invalid token

Got to admit, I am disappointed that

> parseInt("08", 8);

returns 0 instead of NaN

Returning 0 makes perfect sense. parseInt matches an integer from the beginning of the string, so it reads the 0 and then stops at the 8 because 8 is not a valid digit in base 8.

    >>> parseInt("123foobar", 10)
    123

Good point.