javascript - the Date.getMonth() method has bug?

Question

I tested in chrome and firefox, and here is the problem. The Date object's getMonth() method has an Bug? When I set the location date on someDay, like "2013-1-31"

then, the js code is :

var d = new Date();
d.setMonth(8);
d.getMonth();

The result is "9", why?

I found when the month has 31 days, run the setMonth method and the getMonth method will return wrong value

why?

Answer 1

The getMonth() method returns the month (from 0 to 11) for the specified date, according to local time.

Note: January is 0, February is 1, and so on.