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.

▲ dvt 8 hours ago | parent | next [-]

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.

▲ winstonp 10 hours ago | parent | prev | next [-]

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 9 hours ago | parent | prev [-]

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 7 hours ago \| parent \| next [-]
		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 3 hours ago \| parent \| prev [-]
		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.