Bodgan Lucaciu told us a funny story about a strange bug. It’s like this: in Javascript, when you parse a number from a string – let’s say a month’s index like 07 – with parseInt you must be very careful, because, for parseInt, the leading 0 is an indicator that the number is written in octal instead of decimal.

alert(parseInt('07')); // for July - will echo 7
alert(parseInt('08')); // for August - will echo 0 as there is no 08 in octal

So if your application mysteriously stops working on the first of August, this might be your problem. Although this “feature” is marked as deprecated, it’s still present in many modern browsers, so one can never be too careful. Also keep in mind that by default, numbers starting with 0x are considered to be hexadecimals.