Why Does JavaScript\'s `Date` Object Use a Zero-Based Month Index?

Javascript Date Month Discrepancy

In Javascript, the Date object constructor takes a month parameter that represents the month of the year, starting with 0 for January to 11 for December. This is contrary to the common convention of starting months with 1 for January and ending them with 12 for December.

Example

Consider the following code:

var myDate = new Date(2012, 9, 23, 0, 0, 0, 0);
console.log(myDate);

Instead of printing a date in October, as one might expect, it prints the following:

Tue Oct 23 2012 00:00:00 GMT-0400 (Eastern Daylight Time)

This is because Javascript interprets the 9th month parameter as October, since it follows the zero-based indexing for months.

Resolution

To specify a date in October using Javascript, you should use the month index 9, not 10. For example:

var myOctoberDate = new Date(2012, 9, 23, 0, 0, 0, 0);
console.log(myOctoberDate);

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