Project Euler Solution #19 in Javascript

Counting Sundays

You are given the following information, but you may prefer to do some research for yourself.

• 1 Jan 1900 was a Monday.
• Thirty days has September,
• April, June and November.
• All the rest have thirty-one,
• Saving February alone,
• Which has twenty-eight, rain or shine.
• And on leap years, twenty-nine.

A leap year occurs on any year evenly divisible by 4, but not on a century unless it is divisible by 400.

How many Sundays fell on the first of the month during the twentieth century (1 Jan 1901 to 31 Dec 2000)?