Why Does JavaScript's getMonth() Return the Previous Month?

When using a datepicker that provides a date in the format "Sun Jul 7 00:00:00 EDT 2013," you might notice that the getMonth() method returns the previous month. For instance, the code snippet below:

var d1 = new Date("Sun Jul 7 00:00:00 EDT 2013");
d1.getMonth(); //gives 6 instead of 7

The Reason:

The reason for this discrepancy lies in the fact that JavaScript's getMonth() method assigns months a zero-based index. Therefore, January is assigned the value of 0, February is assigned 1, and so on. When calling getMonth() on a date representing July, it actually returns the value for June (6).

Solution:

To obtain the correct month, you can use the following adjusted code:

d1.getMonth()   1; //returns the correct month, which is 7 for July

By adding 1 to the result of getMonth(), you offset the zero-based index and obtain the month as per calendar convention.