validCashtag top-level constant

String const validCashtag

A cashtag is a $ prefixed ticker-like symbol composed of an ASCII letter optionally followed by up to four more ASCII letters or digits, so the symbol itself is 1 to 5 characters long.

This pattern mirrors Bluesky's official CASHTAG_REGEX in @atproto/api so that detection stays consistent with the reference implementation:

/(^|\s|\()\$([A-Za-z][A-Za-z0-9]{0,4})(?=\s|$|[.,;:!?)"'’])/gu

The components are:

1. (^|\s|\() — the leading boundary: the start of the string, any whitespace character (including the ideographic space U+3000 and the no-break space U+00A0), or an opening ASCII parenthesis. This group is captured so the extractor can skip past it to locate the $ mark.
2. $cashSigns — the literal $ mark.
3. ([A-Za-z][A-Za-z0-9]{0,4}) — the ticker symbol, 1 to 5 ASCII chars, where the first character must be a letter.
4. (?=\s|$|[.,;:!?)"'’]) — the trailing boundary lookahead: the symbol must be followed by whitespace, the end of the string, or one of the ASCII punctuation characters . , ; : ! ? ) " ' or the right single quotation mark (U+2019).

Examples that match: $AAPL, $tsla, $BRK1, $F, ($GME). Examples that do NOT match: $1, $-AAPL, $$AAPL, $TOOLONG (over five characters), 日本株$AAPL (no leading boundary) and $AAPLです (no trailing boundary) — matching the official Bluesky behavior, which requires cashtags to be delimited by whitespace, the string edge, (, or ASCII punctuation.

Implementation

const validCashtag =
    r'(^|\s|\()'
    '$cashSigns'
    r'([A-Za-z][A-Za-z0-9]{0,4})'
    '(?=\\s|\$|[.,;:!?)"\'’])';