I think that moment.js was already built that way. For me it kinda makes sense: if days are calculated with a 1-index in mind, why make months different? As I said: it KINDA makes sense.
No, they're 0-indexed in Moment. But yes, the reason I made Luxon 1-index them is that days and years are 1-indexed. I also fielded a lot of issues in Moment that were caused by newer programmers not knowing that months were 0-indexed.
I'm not defending the difference between how months and days/years are treated. But here are some possible reasons.
From ctime(3):
Broken-down time is stored in the structure tm, which is defined in <time.h> as follows:
struct tm {
int tm_sec; /* Seconds (0-60) */
int tm_min; /* Minutes (0-59) */
int tm_hour; /* Hours (0-23) */
int tm_mday; /* Day of the month (1-31) */
int tm_mon; /* Month (0-11) */
int tm_year; /* Year - 1900 */
int tm_wday; /* Day of the week (0-6, Sunday = 0) */
int tm_yday; /* Day in the year (0-365, 1 Jan = 0) */
int tm_isdst; /* Daylight saving time */
};
Well, nobody is confused when their digital watch reads "00:00:00" as the ball drops on New Years Eve. But if the date was 2018-00-01 people would be like "WTF??"
As explained on the website, that's why this is Luxon and not moment 3.0. It's a great approach for them to take that allows them to experiment, grow, and relieve the pressure from calls for change, without disrupting the existing community.
This seems like a bold decision and terrifying source of errors for those of us with decades of experience thinking January is 0.