If you are using this and not Moment.js, then you are on your own.
It's fun to write your own utility, but it's kind of silly to use it in production when there are better solutions out there.
JavaScript clone of MySQL's DATE_FORMAT() function
This function is aimed at providing the functionality of the MySQL DATE_FORMAT() function in JavaScript (see http://dev.mysql.com/doc/refman/5.5/en/date-and-time-functions.html#function_date-format).
formatDate(Date date, String format[, Bool utc]);
date: JavaScript date object to be formatted
format: String containing formatting specifiers (see below)
utc (optional): If true, results are in UTC. If false (default), results are according to local time.
Specifier Description
--------- -----------
%a Abbreviated weekday name (Sun..Sat)
%b Abbreviated month name (Jan..Dec)
%c Month, numeric (0..12)
%D Day of the month with English suffix (0th, 1st, 2nd, 3rd, …)
%d Day of the month, numeric (00..31)
%e Day of the month, numeric (0..31)
%f** Milliseconds (000..999)
%H Hour (00..23)
%h Hour (01..12)
%I Hour (01..12)
%i Minutes, numeric (00..59)
%j* Day of year (001..366)
%k Hour (0..23)
%l Hour (1..12)
%M Month name (January..December)
%m Month, numeric (00..12)
%p AM or PM
%r Time, 12-hour (hh:mm:ss followed by AM or PM)
%S Seconds (00..59)
%s Seconds (00..59)
%T Time, 24-hour (hh:mm:ss)
%U* Week (00..53), where Sunday is the first day of the week
%u* Week (00..53), where Monday is the first day of the week
%V* Week (01..53), where Sunday is the first day of the week; used with %X
%v* Week (01..53), where Monday is the first day of the week; used with %x
%W Weekday name (Sunday..Saturday)
%w Day of the week (0=Sunday..6=Saturday)
%X* Year for the week where Sunday is the first day of the week, numeric, four digits; used with %V
%x* Year for the week, where Monday is the first day of the week, numeric, four digits; used with %v
%Y Year, numeric, four digits
%y Year, numeric (two digits)
%% A literal “%” character
%? ?, for any “?” not listed above
* Not yet supported
** The MySQL DATE_FORMAT() %f specifier returns Microseconds (000000..999999)