regexjavascriptreference
Regular Expressions Cheat Sheet for JavaScript Developers
May 1, 20267 min read
Most developers use regex for the same 15–20 patterns repeatedly. This reference covers the patterns that actually appear in production JavaScript code, with copy-ready snippets and notes on edge cases.
Syntax quick reference
| Pattern | Meaning |
|---|---|
. | Any character except newline (use s flag to include newlines) |
\d / \D | Digit / non-digit |
\w / \W | Word char (A-Za-z0-9_) / non-word |
\s / \S | Whitespace / non-whitespace |
^ / $ | Start / end of string (m flag: start/end of line) |
* + ? | 0 or more / 1 or more / 0 or 1 |
{n} {n,} {n,m} | Exactly n / at least n / between n and m |
(abc) | Capture group — referenced as $1, $2... |
(?:abc) | Non-capturing group — groups but doesn't capture |
(?<name>abc) | Named capture group — referenced as $<name> |
a|b | Alternation: a or b |
[abc] | Character class: a, b, or c |
[^abc] | Negated class: anything except a, b, c |
\b / \B | Word boundary / non-word boundary |
(?=abc) | Positive lookahead: followed by abc |
(?!abc) | Negative lookahead: not followed by abc |
Common patterns
Email address (practical)
/^[a-zA-Z0-9._%+\-]+@[a-zA-Z0-9.\-]+\.[a-zA-Z]{2,}$/Note: the only truly correct email regex spans thousands of characters. For most apps, validate server-side by sending a confirmation email.
URL
/^https?:\/\/[^\s/$.?#].[^\s]*$/i
IPv4 address
/^(25[0-5]|2[0-4]\d|[01]?\d\d?)\.(25[0-5]|2[0-4]\d|[01]?\d\d?)\.(25[0-5]|2[0-4]\d|[01]?\d\d?)\.(25[0-5]|2[0-4]\d|[01]?\d\d?)$/
ISO 8601 date (YYYY-MM-DD)
/^\d{4}-(0[1-9]|1[0-2])-(0[1-9]|[12]\d|3[01])$/UUID v4
/^[0-9a-f]{8}-[0-9a-f]{4}-4[0-9a-f]{3}-[89ab][0-9a-f]{3}-[0-9a-f]{12}$/iSemantic version (semver)
/^(0|[1-9]\d*)\.(0|[1-9]\d*)\.(0|[1-9]\d*)(?:-((?:0|[1-9]\d*|\d*[a-zA-Z-][0-9a-zA-Z-]*)(?:\.(?:0|[1-9]\d*|\d*[a-zA-Z-][0-9a-zA-Z-]*))*))?(?:\+([0-9a-zA-Z-]+(?:\.[0-9a-zA-Z-]+)*))?$/
Hex color code
/^#([0-9a-fA-F]{3}|[0-9a-fA-F]{6})$/Phone number (E.164 international format)
/^\+[1-9]\d{1,14}$/Strong password (min 8 chars, upper + lower + digit + symbol)
/^(?=.*[a-z])(?=.*[A-Z])(?=.*\d)(?=.*[^a-zA-Z\d]).{8,}$/Slug (URL-safe)
/^[a-z0-9]+(?:-[a-z0-9]+)*$/
Flags cheatsheet
g— global: find all matches (not just first). Required forString.matchAll().i— case-insensitivem— multiline:^and$match line boundaries, not string boundariess— dotAll:.matches\ntoou— unicode: enables\p{...}property escapes and correct handling of surrogate pairsd— indices: adds.indicesto match results with start/end positions
Test your patterns interactively
Paste any pattern from above into the regex tester to see live match highlighting, capture group values, and the equivalent Python/Go/PHP code.
Try it yourself
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