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Going back even further in time, Java.util.Date was was heavily inspired by a C library. That’s the origin of getMonth() in Java (and therefore in JS) returnin

• wanderingstan 2y ago
  Just spitballing, but in C it was always the convention to use zero-based indexing. Probably because you were often adding these indexes to pointers (literal memory addresses) to index into an array, so you needed a zero to index into the first slot of the array.
  • 8n4vidtmkvmk 2y ago
    What I don't get is why the day of the month doesn't also start at 0?
• andyjohnson0 2y ago
  C uses zero-based array indexing. A C array variable is a pointer to its first element, and an element index is just an offset from that. Element 0 is at start + 0, element 1 is at start + (1 * element size) etc. Which why the fields of the 'tm' structure [1] (used to represent dates and times) are zero based§. Makes it easy to index into eg an array of day names using tm_wday. I guess at one time Java.util.Date was a leaky abstraction layer on-top of such an api. § Except for the tm_mday element, which curiously is 1-based. I've always assumed that this is because it is unlikely to be used as an array index. A long time ago I'm ashamed to admit that I used tm_mday == 0 as a quick check for an invalid tm value. [1] https://en.cppreference.com/w/c/chrono/tm https://en.cppreference.com/w/c/chrono/tm