Implement formatDate

[DYM-d]

No description provided.

[mateacademy-ai-mentor]

Review Summary

I am requesting changes because the YYYY → YY conversion is currently incorrect and breaks a core requirement of the task. In src/formatDate.js, the logic that converts a 4‑digit year to 2 digits subtracts 1900 from the numeric year instead of taking the last two characters of the year string; this only works accidentally for some years and will produce wrong results for years outside the 1900s. The requirement explicitly states that when going from YYYY to YY, you should "use 2 last digits", so the implementation needs to be updated to derive the 2‑digit year via string slicing (for example, yearString.slice(-2)) rather than arithmetic. This is a critical blocker because it affects the core functionality of the formatter and will cause incorrect output for valid inputs that include years not equal to 19xx.

To fix this, locate the branch in your formatDate function where fromFormat uses YYYY and toFormat uses YY (the YYYY → YY case) and change the year conversion so it takes the last two characters from the year string, e.g. const shortYear = fullYearString.slice(-2);, and then uses that value as the YY part. Make sure this logic works for any 4‑digit year, including 18xx, 19xx, 20xx and beyond, and does not attempt to infer or change the century during truncation. The rest of your implementation — changing separators, reordering parts, and handling YY → YYYY with the 20/19 rule — looks solid and aligns well with the task description. Once you correct the YYYY → YY handling, your solution will fully meet the requirements, and you’re very close to that point already.

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[mateacademy-ai-mentor]

Here, when converting from YYYY to YY, you subtract 1900 from the stringified year, which only works accidentally for some years and does not match the requirement "use 2 last digits"; instead, take the last two characters of the year string (e.g. via slice(-2)) so any 4-digit year is converted correctly to YY.

[mateacademy-ai-mentor]

Review Summary

Your solution is approved because it fully meets the functional requirements for formatDate and matches all checklist items. The function correctly accepts date, fromFormat, and toFormat, uses the separator from fromFormat to split the input string, and the separator from toFormat to join the output, ensuring formats like DD/MM/YY and YYYY-MM-DD are handled as described. You properly reorder the date parts based on the positions of year, month, and day in the format arrays, which satisfies the requirement to support flexible format transformations. Year conversion logic is correctly implemented: YYYY → YY uses slice(-2) on the year string, and YY → YYYY uses 20YY for years under 30 and 19YY otherwise, aligning with [CHECKLIST ITEM #9–#11]. The implementation also follows the constraint of assuming valid input and not adding extra defensive checks, matching [CHECKLIST ITEM #6–#8]. Overall, the function behaves as required and there are no critical blockers, so your work on this task is successfully completed—nice job keeping the logic clean and focused on the specified behavior.

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