function getMonthName(monthNumber) {
const date = new Date();
date.setMonth(monthNumber - 1);
return date.toLocaleString([], { month: 'long' });
}
You want to create the date “31st February”, but it’s JavaScript that’s cursed?
Write a less side-effecty function.
function getMonthName(monthNumber) {
const date = new Date(2023, monthNumber - 1, 1);
return date.toLocaleString([], { month: 'long' });
}
The point is that this scenario exists in Js in the first place. It’s a completely unnecessary rake left around for people to step on. Also, the function isn’t side effecty since it doesn’t make implicit references outside its scope. The fact that the date is mutable is an internal concern there. You could just as easily do
function getMonthName(monthNumber) {
const date = new Date();
date.setDate(1);
date.setMonth(monthNumber - 1);
return date.toLocaleString([], { month: 'long' });
}
The problem here isn’t with side effects, but with having to know that you want to set your date to first day to get the next month reliably.
The rake has nothing to do with JS (which I agree is cursed, but for its own reasons, not this).
You have called a function in a way that does not give a consistent value (Date()). Such functions are hardly the preserve of JavaScript. You’ve failed to adequately deal with the range of values produced, with code that tries to insist that the “31st February” can be a meaningful date in February. You should accept that this is your mistake and learn to (better) avoid side effects where possible.
Also, the function isn’t side effecty since it doesn’t make implicit references outside its scope.
Edit responding to your edit:
Also, the function isn’t side effecty since it doesn’t make implicit references outside its scope.
The Date() function’s output varies according to something other than its input (and even the rest of your program). Using its output without accounting for that variation means that your function, as originally written, also gives inconsistent return values, varying according to something other than its input, because it does, in fact, reference something outside the function. If it did not, the results would only depend on the monthNumber argument, and would always be consistent. I don’t know what you call that, but I view it as a side effect.
As you have said, the rake is that months have different lengths, and you need to account for that. But that’s not one of JavaScript’s many issues.
The idea is to get the current data that will have the current year, month, day in it, and then to query this date for the previous month. A sane API would just throw an error when the date is out of range. A Js API will quitely give you nonsense instead. Again, side effects have absolutely nothing to do with anything here.
