JavaScript Regex Cheat Sheet
A practical JavaScript regular expression cheat sheet covering flags, groups, anchors, and common patterns — with a link to test them live.
Quick start
In JavaScript, regular expressions are written as /pattern/flags or created with new RegExp(). Test patterns against sample text before shipping them into production validation or parsing code.
Common flags
Flags change matching behavior. Use them deliberately — especially g (global) and m (multiline).
- g — find all matches, not just the first
- i — case-insensitive matching
- m — ^ and $ match line boundaries
- s — dot (.) also matches newline
- u — Unicode mode
- y — sticky matching from lastIndex
- d — provide match indices (where supported)
Useful building blocks
Anchors and groups help you write precise patterns without accidental partial matches.
- ^ / $ — start / end of string (or line with m)
- \d \w \s — digit, word character, whitespace
- . — any character (except newline unless s)
- (...) — capturing group
- (?:...) — non-capturing group
- (?<name>...) — named capture group
- ? + * {n,m} — quantifiers
Test before you trust
Regex bugs are easy to miss with hand-picked examples. Use a live tester to inspect matches, capture groups, and replacements against realistic sample text — including edge cases and empty input.