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marcosdumay • yesterday at 7:30 PM • 2 replies • view on HN

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.

Replies

jazzyjackson • yesterday at 9:56 PM

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 • today at 1:58 AM

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.