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Character counting in JavaScript for textarea inputs can mismatch with server-side validation due to multiple issues beyond surrogate pairs. When form data is submitted via HTTP, newlines are normalized from \n to \r\n, causing discrepancies between JavaScript's count and PHP/MySQL validation. Other pitfalls include lone surrogates causing MySQL errors, NFD normalization from older macOS systems, and choosing the wrong counting method. While [...str].length handles surrogate pairs, it doesn't account for newline normalization. Intl.Segmenter counts visual characters but doesn't match MySQL's CHAR_LENGTH(). The solution involves normalizing newlines to CRLF before counting and excluding invalid surrogates to match MySQL's behavior.

Beyond Surrogate Pairs: Hidden Pitfalls in JS Character Counting with PHP/MySQL

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