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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 2 years ago by 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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[–] 21 points 2 years ago

The legacy Date object has many problems and this is one of them. Another infamous one is that it uses zero-based month numbers: January is the zeroth month and December the 11th month.

This will be fixed Any Day Now™️ when Temporal is released. This is a carefully designed library that supersedes Date and is currently waiting on some standards to be finalized.

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