parseISO - parsing invalid string into a valid date

[MBelniak]

Hi.
I've come across this issue while using date-fns.
Current behaviour:
parseISO('2016-03-16T08 ooo') // returns Date(Wed Mar 16 2016 08:00:00 GMT+0100 (CET))
Expected behaviour (at least momentjs and some online regex-based parsers):
parseISO('2016-03-16T08 ooo') // returns Invalid Date
Is this actually a bug or for some reason current bahaviour is the expected one?

[imballinst]

@kossnocorp is this intended behavior? From a quick glance on parseISO, it uses RegEx to parse the date and time. I think in this case, it only "partially parses" the invalid string. CMIIW!

[kossnocorp]

I've no strong opinion regarding this, to be honest. As I see, not only Moment.js behaves like that:

new Date('2016-03-16T08 ooo')
//=> Invalid Date
Date.parse('2016-03-16T08 ooo')
//=> NaN

So I guess this is a bug.

[imballinst]

Alright, thanks for the clarification! I'll try attempting on this issue.

[kossnocorp]

@imballinst thanks 🙏

[dojchek]

I think there may be another 'case' of this issue. It successfully parses the two digits number.
parseISO('33') // Fri Jan 01 3300 00:00:00 GMT+0100 (Central European Standard Time)

'33' is not a valid ISO string (https://en.wikipedia.org/wiki/ISO_8601), so I think it should fail and return 'Invalid Date'
Interestingly, one digit or three or more digits numbers fail to parse with 'Invalid Date' being returned.

parseISO('3')     // Invalid Date
parseISO('333')  // Invalid Date

[imballinst]

@dojchek noted -- thanks for the information! I'll try handling that case as well in my PR.

[imballinst]

@dojchek it seems like the 2 digits are used to represent centuries, so I guess that's intended?

date-fns/src/parseISO/test.js

Lines 103 to 120 in 4cf918f

	it('parses century 1 BC - 99 AD', () => {
	const result = parseISO('00')
	const date = new Date(0, 0 /* Jan */, 1)
	date.setFullYear(0)
	assert.deepEqual(result, date)
	})
	it('parses centuries after 9999 AD', () => {
	const result = parseISO('+0123')
	assert.deepEqual(result, new Date(12300, 0 /* Jan */, 1))
	})
	it('allows to specify the number of additional digits', () => {
	const result = parseISO('-20', { additionalDigits: 0 })
	const date = new Date(-2000, 0 /* Jan */, 1)
	date.setFullYear(-2000)
	assert.deepEqual(result, date)
	})

CMIIW @kossnocorp

[dojchek]

@imballinst Yes, I also think that's intended - although not very intuitive..
I found only one reference to this format in wiki article which says:
One may simply write "1981" to refer to that year or "19" to refer to the century from 1900 to 1999 inclusive

So it is in fact a valid ISO date. I still need this to "fail" in my use case - so I will check it with some regex or simply check the length of string before doing parseISO, since I only work with dates like 2020-06-26 and 2020-06-26T04:33:26+00:00.

Thank you very much for checking this out