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Comment by mkotowski | Hacker News Reader

That does remind me: why that even is a thing? Ordering days of a week from zero can make sense since there is Monday/Sunday as a week start divide, and this can be seen as a bypass (0/7 as Sunday and 1 as a Monday), but with months?

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Zero indexing for arrays/collections generally makes sense. If you had the months in a normal array they would obviously be zero-indexed (unless you deliberately put a placeholder value in the first position in the array, which would be pretty weird since all the normal ways of getting the first thing in the array would break).

The reason it apparently feels weird to many people to have months be zero indexed is that months are often referred to by their ordinal number, and ordinal numbers obviously start at 1.

> months are often referred to by their ordinal number

What do you mean by “often”? Humans always use ordinal numbers for counting things like months, days, weeks, etc. There is no concept of 0 to be applied here, except for programming array indexing purposes.

Lay people indicate the month with an ordinal all the time since it's how dates are standardized (12/30/2021). People don't often indicate the day of the week with a number, they use "Monday" or "Tuesday". So there's no strongly held convention in people's minds about how to number days like there is for months.

What I mean is that people use the ordinal number as the name of the month (as well as the day of the month). If you ask someone their birthday they’ll often say something like “five twenty, nineteen eighty-four.”

This is a potential cause for confusion when writing computer code, because it’s very common for code to refer to items in a collection starting at zero.

It is lifted from C's struct tm. If you're maintaining tables of month names you're going to 0-index them so tm_mon is 0-based to facilitate that.

Side note regarding humans: I was in a hotel in France that referred to the ground floor as "floor zero" in their elevator. The only time I've ever seen zero used to count something IRL.

This is actually a decent way to demonstrate why zero-indexing for arrays makes sense. If your friend gives you instructions to their apartment “go to the elevator in the lobby and go up 3 floors,” which button do you press in the elevator?

I don’t follow? Even in your specific example, it would be +3 to whatever floor the elevator says you’re currently on. Though, usually people refer to the exact floor number per the elevator signs.

Even if this is true, days in JS still start at 1. It is inconsistent.

Zero indexing of arrays only makes sense in C because array variable is a pointer to first element of the array. In all languages that have actual array type with length and bounds checking, 1 would be a better way to index arrays most of the time and having specified valid range would be the best way.

The week starts on Monday in most of the world.

Date & time APIs must match local reality.

When reality differs by locales, at least one "local reality" won't match the API.

https://stackoverflow.com/a/41992352

> it was copied from Java's JDK1.0 (1995) java.util.Date, which also had this quirk

No. It’s definitely older than that.

https://mobile.twitter.com/hillelogram/status/13292284196289...

Just because the issue predated Java doesn’t preclude the fact that the initial JavaScript Date implementation was lifted from java.util.Date. Brandon Eich has explicitly stated it was so.

https://maggiepint.com/2017/04/09/fixing-javascript-date-get...

Twitter is such a bad platform for this. Code in images means it's completely inaccessible to the blind and very inaccessible to people with poor vision, and you can't copy and paste it into an editor for syntax highlighting or better examination.

https://twitter.com/bahstgwamt/status/867609109276872704?s=2...

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