this post was submitted on 06 Nov 2023
1 points (100.0% liked)

Programmer Humor

42036 readers
74 users here now

Post funny things about programming here! (Or just rant about your favourite programming language.)

Rules:

founded 6 years ago
MODERATORS
AgreeableLandscape@lemmy.ml
cat_programmer@lemmy.ml
1
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 yogthos@lemmy.ml to c/programmerhumor@lemmy.ml
6 comments fedilink hide all child comments
 
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.

you are viewing a single comment's thread
view the rest of the comments
[โ€“] aebletrae@hexbear.net 0 points 2 years ago (1 children)

You've replied while I was editing, so see that regarding what I mean by side effects.

As far as throwing an error when you try to create "31st February", this wouldn't actually help much, since the error would still only occur on some days of the year, because your original code doesn't account for the range of outputs from Date() when called without arguments.

To perform correctly, your code needs to normalise the day of the month, or just create the date more explicitly to begin with, but this is a calendrical issue, not a JavaScript one.

[โ€“] yogthos@lemmy.ml 1 points 2 years ago

Side effects are when your function has a reference to some state outside its scope and modifies that state. A function that produces different outputs when it's called, such as getting a current time is not an example of a side effect. Again, the issue here is that Js tries to infer what to do with a bad input, a number outside acceptable range, instead of simply rejecting it.

My point isn't that you can't write a better function that's less error prone, but the fact that Js allows such things to happen in the first place. It's a very easily avoidable problem at the API level.