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JavaScript Gotchas: Default Array.sort, == Coercion, parseInt in map, Date Parsing and var in Loops

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Self-Hosting & Infra beginner 6 min read $0.01 Updated 2026-10-20

Node 22 outputs: [10,9,100].sort(), numeric compare function, loose equality results, Number versus parseInt versus parseFloat, Date parsing of 2026-10-20 as UTC, 2026-02-30 becoming March 1, includes versus indexOf for NaN, and let versus var closures.

Run the classic JavaScript surprises and learn their fixes: sort() comparing text, ["1","2","3"].map(parseInt), invalid dates rolling over, date-only strings parsed as UTC, NaN checks and closures in var loops.

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#javascript#gotchas#dates#sorting#coercion

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