fix(isISO8601): route signed ordinal dates to the day-of-year check

[yfwmaniish]

Fixes #2860.

What

isISO8601(str, { strict: true }) misroutes signed ordinal dates (+YYYY-DDD / -YYYY-DDD).

isValidDate()'s ordinal branch matches:

const ordinalMatch = str.match(/^(\d{4})-?(\d{3})([ T]{1}\.*|$)/);

This has no sign prefix, even though the top-level iso8601 regex explicitly accepts a leading +/- on the year ([\+-]?\d{4}). A signed ordinal date like "+2009-145" fails this ^(\d{4}) match (the string starts with +, not a digit) and falls through to the generic calendar-date split:

const match = str.match(/(\d{4})-?(\d{0,2})-?(\d*)/).map(Number);

This regex has no ^ anchor, so it matches starting one character in, cutting the 3-digit day-of-year into a 2-digit "month" and 1-digit "day". Two things follow:

• "+2009-145" → month=14, day=5 → new Date('2009-14-05') normalizes the out-of-range month, the equality check fails, and a valid date (day 145 of 2009 exists) is rejected.
• "+2009-130" → month=13, day=0 → day is falsy, so if (month && day) is skipped entirely and the function unconditionally returns true — the day-of-year is never actually validated, only coincidentally correct here.

Fix

Add [+-]? to the ordinal pattern, so signed ordinal dates route to the branch that already has the correct leap-year-aware day-of-year check (unaffected — the capture group indices don't change, so the existing oYear/oDay extraction is unchanged).

Testing

Added '+2009-145', '+2009-130', '-2009-145' to the strict = true valid cases in test/validators.test.js.

• Negative control: reverted just the regex change and reran — +2009-145 fails with exactly the reported symptom (validator.isISO8601("+2009-145", {"strict":true}) failed but should have passed); restored.
• Full suite: npx mocha --require @babel/register --reporter dot --recursive — 323/323 passing.
• eslint on both changed files — clean.

I didn't add an invalid case: the only way to reach an "impossible day-of-year" here is day 366 in a non-leap year, and the top-level iso8601 regex's own day-of-year alternative (3([0-5]\d|6[0-6])) already constrains matches to 001-366, so a genuinely out-of-range day like 999 never reaches this code at all regardless of the fix (rejected earlier, by the outer regex). There's no black-box example where this specific bug flips a wrong accept into a rejection — only wrong rejections (+2009-145) and an unvalidated-but-coincidentally-correct pass-through (+2009-130), both covered above.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (a79ff98) to head (4cf7de6).

Additional details and impacted files

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  Files          114       114           
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[Copilot]

Pull request overview

This PR fixes isISO8601(str, { strict: true }) rejecting signed ordinal dates (+YYYY-DDD / -YYYY-DDD) by ensuring those inputs route through the ordinal (day-of-year) validation path in src/lib/isISO8601.js, instead of falling through to the generic calendar-date parsing.

Changes:

• Updated the ordinal-date detection regex in isValidDate() to allow an optional leading +/- sign before the year.
• Added strict-mode regression cases for signed ordinal dates to the validator test suite.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
src/lib/isISO8601.js	Allows optional leading sign in the ordinal-date match so signed ordinal inputs use the correct leap-year-aware day-of-year validation.
test/validators.test.js	Adds strict-mode valid test cases covering signed ordinal dates to prevent regressions.

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