parse_date_code is off by 1 month

[teohhanhui]

Value returned from SSF.parse_date_code has m (month) value offset by +1.

moment.fromOADate (moment-msdate plugin) gives the correct value.

[SheetJSDev]

tl;dr parse_date_code returns one-based month numbers and JS uses zero-based month numbers. This is simpler than making adjustments elsewhere.

The intention of the parse_date_code function is to return the values that you would use in rendering a date output (including corrections for the 1900 leap year ). Since other sources do not try to make 1900 a leap year, I generally don't recommend using this if you have a date code from a source other than a spreadsheet.

The m value from parse_date_code gives you the 1-indexed month value, consistent with string renderings of the m and mm format. For example, today is "October 20 2016" date code 42663 according to Excel. There are 5 month formats, from m to mmmmm. If you want to compare, try using the format m , mm , mmm , mmmm , mmmmm:

value	date	m , mm , mmm , mmmm , mmmmm
42663	10/20/16	10 , 10 , Oct , October , O
42419	2/19/16	2 , 02 , Feb , February , F

JS dates use zero-indexed months, which is why parse_date_code seems to give you a different month. It was a design decision. For what it's worth, it seems inconsistent for getDate to return a one-based day and for getMonth to return a zero-based month.