If you run this JavaScript function on the 31st of a month, the result will be a month off. The best part is that this is the intended behvaior. JavaScript is a cursed language. (lemmy.ml)

submitted 10 months ago by yogthos@lemmy.ml to c/programmerhumor@lemmy.ml

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function getMonthName(monthNumber) {
  const date = new Date();
  date.setMonth(monthNumber - 1);

  return date.toLocaleString([], { month: 'long' });
}

The current day of month will have an impact on the behavior of this method. Conceptually it will add the number of days given by the current day of the month to the 1st day of the new month specified as the parameter, to return the new date. For example, if the current value is 31st January 2016, calling setMonth with a value of 1 will return 2nd March 2016. This is because in 2016 February had 29 days.

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[-] ftatateeta@lemmy.ml 1 points 10 months ago

I would expect the month to increment by one and the day to be clamped to the valid days for the month.

[-] yogthos@lemmygrad.ml -3 points 10 months ago

That's precisely what I'd expect as well, and what APIs in languages like Java do.

this post was submitted on 06 Nov 2023

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