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/error/iNotes
Fast and readable when the pattern is static.
Regex in JavaScript
JavaScript RegExp syntax, APIs, flags, named captures, and high-value browser/Node recipes.
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JavaScript Regex APIs
Core JavaScript regex syntax and methods.
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new RegExp("^" + prefix + "\\d+$", "i")Notes
Useful when the pattern is assembled at runtime.
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/error/i.test(message)Notes
Returns `true` or `false`.
exec() detailed match
Get captures and index information from a match.
javascriptANYjavascriptapiexec
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/(\d{4})-(\d{2})-(\d{2})/.exec(dateStr)Notes
Returns an array-like match object or `null`.
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text.match(/\b\w+\b/g)Notes
With `g`, returns all matches; without `g`, returns the first detailed match.
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Array.from(text.matchAll(/(?<key>\w+)=(?<val>\w+)/g))Notes
Useful when you need every match and capture groups.
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text.replace(/\s+/g, " ")Notes
Common for cleanup and normalization.
replace() callback
Compute replacements dynamically from captures.
javascriptANYjavascriptapireplace
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text.replace(/(\w+),\s*(\w+)/g, (_, last, first) => `${first} ${last}`)Notes
Useful for reformatting structured text.
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csvLine.split(/\s*,\s*/)Notes
Removes optional whitespace around commas.
JavaScript Flags and Captures
Flags, named captures, and replacement patterns in JavaScript.
Common JS flags
Global, ignore-case, multiline, dotAll, Unicode, sticky, indices.
javascriptANYjavascriptflags
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/pattern/gimsuydNotes
JavaScript supports several flags; combine only the ones you need.
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/(?<year>\d{4})-(?<month>\d{2})-(?<day>\d{2})/Notes
Read captures using `match.groups.year` in modern runtimes.
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/(?<q>["\']).*?\k<q>/Notes
Useful for matching paired quotes.
Replacement with numbered groups
Use `$1`, `$2`, etc. in replacement strings.
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text.replace(/(\w+)\s+(\w+)/, "$2, $1")Notes
Convenient for simple reordering.
Replacement with named groups
Use a replacement callback to access named captures clearly.
javascriptANYjavascriptreplacenamed
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text.replace(/(?<h>\d{2}):(?<m>\d{2})/, (...args) => { const groups = args.at(-1); return `${groups.h}h ${groups.m}m`; })Notes
Named groups improve readability in larger replacements.
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/^\p{L}+$/uNotes
Requires the `u` flag.
JavaScript Recipes
High-value browser and Node regex recipes.
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/^[^\s@]+@[^\s@]+\.[^\s@]+$/Notes
A lightweight client-side check, not a full RFC parser.
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/^[a-z0-9]+(?:-[a-z0-9]+)*$/Notes
Good for URLs, IDs, and content slugs.
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/([^&=?#]+)=([^&=#]*)/gNotes
Use `matchAll` to iterate all pairs.
Collapse internal whitespace
Normalize repeated whitespace down to single spaces.
javascriptANYjavascriptcleanupwhitespace
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text.trim().replace(/\s+/g, " ")Notes
Very common cleanup recipe.
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text.replace(/\bBearer\s+[A-Za-z0-9._-]+\b/g, "Bearer [REDACTED]")Notes
Useful when sanitizing output.
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/#(?:[0-9A-Fa-f]{3}|[0-9A-Fa-f]{6}|[0-9A-Fa-f]{8})\b/gNotes
Covers 3, 6, and 8 digit forms.
Basic semver parser
Extract version parts from a semantic version string.
javascriptANYjavascriptversionssemver
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/^(?<major>0|[1-9]\d*)\.(?<minor>0|[1-9]\d*)\.(?<patch>0|[1-9]\d*)(?:-[0-9A-Za-z.-]+)?(?:\+[0-9A-Za-z.-]+)?$/Notes
Handy for tooling and validation.
More in Regex
Regex Examples and Cookbook
Large cookbook of validation, extraction, cleanup, and code-search regex recipes for everyday engineering work.
Regex for VS Code and IDE Search
Regex patterns and search/replace recipes for VS Code, JetBrains IDEs, and common editor refactors.
Regex for PCRE, grep, ripgrep, and sed
Regex patterns and command-line workflows for grep, ripgrep, sed, awk, and advanced PCRE-style features.
Regex Cheat Sheet
Core regular expression syntax, classes, quantifiers, groups, lookarounds, flags, and performance techniques.