Date-format

[petrenko1694-spec]

No description provided.

[mateacademy-ai-mentor]

Review Summary

I am requesting changes because there is one critical behavior that conflicts with the explicit requirements and the intended use of the format arrays. In src/formatDate.js, your separator handling both (1) tries to infer the separator by scanning the date string and (2) includes a sep === undefined / "Wrong separator!" path; this is effectively input validation, which the task explicitly says not to do, and it ignores that the separator is defined directly in fromFormat[fromFormat.length - 1]. To align with the requirements, you should remove the validation/error branch entirely and simply set the separator as const sep = fromFormat[fromFormat.length - 1];, then split/join using that value instead of inspecting characters in the input date. This change will also fully satisfy the checklist items that say the format arrays themselves describe the separator and that we should assume correct input.

A smaller, non-blocking improvement: when expanding YY to YYYY, your line obj['YYYY'] = obj['YY'] < 30 ? '20' + obj['YY'] : '19' + obj['YY']; relies on implicit string-to-number coercion; consider writing Number(obj['YY']) < 30 to make the numeric intent explicit and avoid subtle type issues. Overall, your handling of reordering, separator changes, and year-length conversion is solid; once you simplify the separator logic and remove the validation branch, this will cleanly meet all stated requirements.

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[mateacademy-ai-mentor]

sep is initialized to an empty string and then later checked against undefined, which can never be true here; this also adds unnecessary validation despite the task stating there is no need to validate input. Consider removing this check and deriving the separator directly from fromFormat instead of scanning date.

[mateacademy-ai-mentor]

The separator is inferred from the characters in date and compared to fromFormat[fromFormat.length - 1], but the task states that the format arrays themselves describe the separator. It would be clearer and more reliable to use const sep = fromFormat[fromFormat.length - 1]; instead of inspecting the input string.

[mateacademy-ai-mentor]

obj['YYYY'] = obj['YY'] < 30 ? '20' + obj['YY'] : '19' + obj['YY']; relies on implicit numeric coercion of the string obj['YY']. Given assumptions about valid input this likely works, but making the comparison numeric explicitly would better reflect the requirement YY < 30 and avoid subtle type issues.

[mateacademy-ai-mentor]

Review Summary

I am approving your solution because it correctly implements all the required behavior for formatDate: parsing based on fromFormat, reordering according to toFormat, changing separators, and handling both YYYY → YY and YY → YYYY conversions with the specified 20xx/19xx rule. Functionally, your code now satisfies the task requirements and should work for the expected valid inputs.

The only remaining point is a minor style/clarity improvement: in the YY to YYYY conversion logic (where you compare obj['YY'] < 30), you are relying on implicit string-to-number coercion. While this works given the assumptions, it is clearer and safer to write something like Number(obj['YY']) < 30 so future readers immediately see the numeric intent. This is not a blocker, but it’s a good habit to avoid subtle type issues in JavaScript. Overall, well done on aligning the implementation closely with the specification and refining it based on earlier feedback.

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[mateacademy-ai-mentor]

When converting YY to YYYY, this comparison relies on implicit string-to-number coercion; consider using Number(obj['YY']) < 30 to make the numeric intent explicit and avoid subtle type issues.