Regular Expression for all non letter changes to underscore remain fixed first letter # intact

I use this regex for changing all symbols or any non digit character to underscore remaining first # value as it is.

text.replace(/(?!^)[^\p{L}\p{N}]+/gu, '_');

This will working fine but for bengali letter when user type চার it prints like that: চ__া_র

Please provide me the correct regex.

The second char (\u09BE) is a 09BE BENGALI VOWEL SIGN AA that belongs to a "Mark, spacing combining" Unicode category (Mc).

That means, you need to add a diacritic mark Unicode category class to the negated character class:

/(?!^)[^\p{L}\p{N}\p{M}]+/gu

See the JavaScript demo:

<!-- begin snippet: js hide: false console: true babel: false -->

<!-- language: lang-js -->

console.log("চার".replace(/(?!^)[^\p{L}\p{N}\p{M}]+/gu, '_'))

<!-- end snippet -->