3 ms·

You might want to play with https://jsdate.wtf/ https://jsdate.wtf/ One can't fathom how weird JS Date can be.

publicdebates 9mo ago
Guessed 2 of the first 3 questions. Got to question 4 and gave up: new Date("not a date") 1) Invalid Date 2) undefined 3) Throws an error 4) null There's literally no way of guessing this crap. It's all random.
- winstonp 9mo ago
  the new Date() constructor is an amalgamation of like 5 different specs, and unless the input matches one of them, which one kicks in is up to the implementer's choice
- marcosdumay 9mo ago
  The choice here is really surprising. I was half-expecting NaN, that you omitted. Is there any other instance of the standard JS library returning an error object instead of throwing one? I can't think of any.
  - jazzyjackson 9mo ago
    I think NaN itself is a bit of an error object, especially in how it's passed through subsequent math functions, which is a different choice than throwing up. But besides that I think you're right, Invalid Date is pretty weird and I somehow never ran into it. One consequence is you can still call Date methods on the invalid date object and then you get NaN from the numeric results.
  - WorldMaker 9mo ago
    The fun trick is that Invalid Date is still a Date: > let invalid = new Date('not a date') > invalid Invalid Date > invalid instanceof Date true You were half-correct on expecting NaN, it's the low level storage of Invalid Date: > invalid.getTime() NaN Invalid Date is just a Date with the "Unix epoch timestamp" of NaN. It also follows NaN comparison logic: > invalid === new Date(NaN) false It's an interesting curio directly related to NaN.
    - tyilo 9mo ago
      > Invalid Date is just a Date with the "Unix epoch timestamp" of NaN. It also follows NaN comparison logic: > > > invalid === new Date(NaN) > false This is just because a JS Date is an object and have nothing to do with the inner representation. > new Date(0) === new Date(0) false
- dvt 9mo ago
  I had no idea we even had an `Invalid Date` object, that's legitimately insane. Some other fun ones: new Date(Math.E) new Date(-1) are both valid dates lol.
- just6979 9mo ago
  I think you got it backwards. The only way is guessing, it's all random. It's the internal inconsistencies that get me. Like, OK, I understand that there might be some quirks, maybe due to some weird backwards compatibility or technical limitation, but there are multiple incompatible quirks _inside_ this single interface! It's terrible, and things like this are a huge part of the reason JS was long considered (and sometimes still is) a Not So Good language.

Guessed 2 of the first 3 questions. Got to question 4 and gave up: new Date("not a date") 1) Invalid Date 2) undefined 3) Throws an error 4) null There's literally no way of guessing this crap. It's all random.

winstonp 9mo ago
the new Date() constructor is an amalgamation of like 5 different specs, and unless the input matches one of them, which one kicks in is up to the implementer's choice
marcosdumay 9mo ago
The choice here is really surprising. I was half-expecting NaN, that you omitted. Is there any other instance of the standard JS library returning an error object instead of throwing one? I can't think of any.
- jazzyjackson 9mo ago
  I think NaN itself is a bit of an error object, especially in how it's passed through subsequent math functions, which is a different choice than throwing up. But besides that I think you're right, Invalid Date is pretty weird and I somehow never ran into it. One consequence is you can still call Date methods on the invalid date object and then you get NaN from the numeric results.
- WorldMaker 9mo ago
  The fun trick is that Invalid Date is still a Date: > let invalid = new Date('not a date') > invalid Invalid Date > invalid instanceof Date true You were half-correct on expecting NaN, it's the low level storage of Invalid Date: > invalid.getTime() NaN Invalid Date is just a Date with the "Unix epoch timestamp" of NaN. It also follows NaN comparison logic: > invalid === new Date(NaN) false It's an interesting curio directly related to NaN.
  - tyilo 9mo ago
    > Invalid Date is just a Date with the "Unix epoch timestamp" of NaN. It also follows NaN comparison logic: > > > invalid === new Date(NaN) > false This is just because a JS Date is an object and have nothing to do with the inner representation. > new Date(0) === new Date(0) false
dvt 9mo ago
I had no idea we even had an `Invalid Date` object, that's legitimately insane. Some other fun ones: new Date(Math.E) new Date(-1) are both valid dates lol.
just6979 9mo ago
I think you got it backwards. The only way is guessing, it's all random. It's the internal inconsistencies that get me. Like, OK, I understand that there might be some quirks, maybe due to some weird backwards compatibility or technical limitation, but there are multiple incompatible quirks _inside_ this single interface! It's terrible, and things like this are a huge part of the reason JS was long considered (and sometimes still is) a Not So Good language.