Question

Looking over the previous questions and answers it appeared this should work :

var palindrome = new Date('2011-11-11');
var december = new Date('2011-11-11');

december.setDate(palindrome.getDate()+20); 
//should be december, but in fact loops back over to Nov 1st)

my jsFiddle

is there a simple way to ensure that months are incremented correctly, or have I missed something obvious ?

Answer 1

The getMonth() call returns a value between 0 and 11, where 0 is January and 11 is December, so 10 means November. You need to increment the value by 1 when using it in a string. If you simply output it as a string you’ll see that it has the correct date. Note I also had to change the starting date format. It didn’t seem to like 2011-11-11 so I made it 11/11/2011. http://jsfiddle.net/9HLSW/