new Date('yyyy-m-d') gives incorrect result

[borgsmidt]

• v10.1.0:
• Darwin Kernel Version 17.5.0: root:xnu-4570.51.1~1/RELEASE_X86_64 x86_64:
• new Date():

// Correct
> new Date('2018-02-01')
2018-02-01T00:00:00.000Z

// Incorrect
> new Date('2018-2-1')
2018-01-31T23:00:00.000Z

// Consistent with first example
> new Date('2018-12-12')
2018-12-12T00:00:00.000Z

[AyushG3112]

According to the ECMAScript Spec:

The function first attempts to parse the format of the String according to the rules (including extended years) called out in Date Time String Format (20.3.1.15). If the String does not conform to that format the function may fall back to any implementation-specific heuristics or implementation-specific date formats.

[ChALkeR]

> new Date('2018-02-01')
2018-02-01T00:00:00.000Z
> new Date('2018-2-1')
2018-01-31T21:00:00.000Z
> new Date('2018-2-1Z')
2018-02-01T00:00:00.000Z

Looks timezone-dependent. I'm in UTC+3 timezone, and I guess that @borgsmidt is in UTC+1?
From what I see, '2018-02-01' is treated as being in UTC, while '2018-2-1' (invalid) is treated as being in local TZ if no offset specified.

[AyushG3112]

@ChALkeR it gets stranger though.

>  new Date("2018-2-31")
2018-03-03T00:00:00.000Z

[Trott]

This is behavior that Node.js inherits from the underlying JavaScript engine (Google's V8 in the official releases). You will see the same behavior if you use Chrome's console. It seems that this behavior is spec-compliant. If it were to change, it would change in V8, not directly in Node.js. So an issue would have to be opened on the V8 issue tracker. (But I suspect such a request would be rejected.)

I'm going to close this, but feel free to re-open (if GitHub lets you) or leave a comment if there's unresolved issues here that I'm failing to realize.

[ChALkeR]

@AyushG3112 There are 28 days in Februrary this year, so 2018-02-31 is actually 2018-03-03.

Also, this is what it looks like for me (seems in line with the above):

> new Date("2018-3-3")
2018-03-02T21:00:00.000Z
> new Date("2018-2-31")
2018-03-02T21:00:00.000Z
> new Date("2018-2-31Z")
2018-03-03T00:00:00.000Z
> new Date("2018-02-31")
2018-03-03T00:00:00.000Z