The hard part of batch date conversion isn't formatting — it's deciding what `01/02/2024` means

I used to think a bulk date converter was basically a dropdown wrapped around a date library. Paste a bunch of rows, pick YYYY-MM-DD , done. Then you look at real exports from spreadsheets, CRMs, logs, and old internal tools and realize the problem isn't "formatting" at all. It's triage. Some rows are obvious. Some are malformed. Some have month names. Some came from a CSV with five unrelated columns. And then there's the classic cursed input: 01/02/2024 , which is either January 2 or February 1 depending on who produced the file. The Vue component behind this tool is interesting because it doesn't pretend that ambiguity goes away if you call the right parser. It models that ambiguity explicitly. It starts by assuming uploaded files are messy, not clean One thing I liked in the source is that it doesn't treat file input as a single happy path. If you upload a TXT file, it works line by line. If the upload looks CSV-ish, it switches into a tiny parser and then tries to figure out which column is actually the date column. The CSV split logic is manual instead of using a naive line.split(",") , which matters because quoted commas are a real thing in exports: const splitCsvLine = ( line ) => { const result = []; let cur = "" ; let inQuotes = false ; for ( let i = 0 ; i < line . length ; i ++ ) { const ch = line [ i ]; if ( ch === ' " ' ) { if ( inQuotes && line [ i + 1 ] === ' " ' ) { cur += ' " ' ; i ++ ; } else { inQuotes = ! inQuotes ; } } else if ( ch === " , " && ! inQuotes ) { result . push ( cur ); cur = "" ; } else { cur += ch ; } } result . push ( cur ); return result . map (( s ) => s . trim ()); }; After that, it doesn't ask the user to map columns immediately. It scores each column by counting how many cells look like dates, then auto-selects the best candidate: for ( let c = 0 ; c < maxCols ; c ++ ) { const count = dataRows . filter (( r ) => isLikelyDateCell ( r [ c ])). length ; columns . push ({ index : c , header : headerRow ? headerRow [ c ] : "" }); i