isISO8601 does not support dates with year inferior to 1000 in strict mode

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Assessment

Difficulty
2/5
Estimated time
1-3 hours
Newbie friendliness
78/100
Issue type
Bug
Clarity
Clearly specified
Activity status
Active
Tech stack
javascript
Domain
backend

Research direction

Start in src/lib/isISO8601.js and inspect the isValidDate function, especially how the year, monthString, and dayString are used to construct the Date object in strict mode. Verify the behavior with the reported 0001-01-13T00:00:00.000Z example; done means valid years below 1000 pass strict validation without breaking existing ISO 8601 checks.

Written by the indexing model from the issue text.

Description

🐛 bug

Describe the bug
When giving a valid date with year before 1000, the isISO8601 validator is returning false when strict option is set to true.
The issue in the isValidDate function of the src/lib/isISO8601.js file.
image
At line 30, a new Date object is instanced using a string built with year, monthString and dayString.
But contrary to month and day, no leading zeros are added to year. This is causing the object Date to not parse correctly the date and in resulting in the d.getUTCFullYear() === year test to fail.

Examples
Using the valid date 0001-01-13T00:00:00.000Z, the parsed year variable will be equal to 1, month to 1 and day to 13.
The Date object will be constructed using the following string: 1-01-13.
This is interpreted as January 1st 2013 instead of January 13th 0001 which obviously lead to the d.getUTCFullYear() === year test to fail (2013 is different than 1)

Additional context
Validator.js version: v13.12.0
Node.js version: v22.12.0
OS platform: linux

Dominant language
JavaScript
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