⌘ K
javascript · ecmascript · runnable · local

Generate JavaScript code from a regex

Drop a pattern in, pick flags, and get a ready-to-paste snippet with test, match, matchAll, replace, and split — using both the regex literal and the RegExp constructor.

Regex → JavaScript
//g
JavaScript
const input = "Reach alice@example.com or bob@test.org.";

const re = /\\b\\w+@\\w+\\.\\w+\\b/g;
const reDynamic = new RegExp("\\\\b\\\\w+@\\\\w+\\\\.\\\\w+\\\\b", "g");

const hasMatch = re.test(input);
const first = input.match(re);
const all = [...input.matchAll(new RegExp("\\\\b\\\\w+@\\\\w+\\\\.\\\\w+\\\\b", "g"))];
const replaced = input.replace(re, "[email]");
const parts = input.split(re);

console.log({ hasMatch, first, all, replaced, parts });
Quick Start

How to use a regex in JavaScript

Two forms: the inline literal /pattern/flags and the dynamic new RegExp(string, flags) constructor. Each has tradeoffs around escaping.

  1. 01

    Type a pattern

    Drop your regex pattern in. Backslashes are doubled in the constructor form but written once in the literal form.

    Patterns are parsed with the JavaScript RegExp constructor, so syntax errors surface immediately and engine quirks like Unicode property escapes (\p{L}) require the u flag.

    patternECMAScriptliteralregex
    input · literalpattern · regex
    /\b\w+@\w+\b/g
    loaded · ECMAScripttarget · ready
  2. 02

    Tune flags + sample

    Toggle g, i, m, s, u, y, d. Edit the sample input to see how each flag changes behaviour.

    Each flag character mirrors the ECMAScript literal: g enables iteration, i folds case, m anchors per line, s lets . match newlines, u unlocks proper Unicode, y is sticky, and d emits indices.

    flagssampleg · i · mlive
    config · optionsflags · flags
    g · i · u
    flags applied · livelive · preview
  3. 03

    Read the snippet

    The output includes literal and constructor forms, test/match/matchAll/replace/split, all in one block ready to paste.

    The generator rewrites the regex for the target language — handling string-literal escaping, raw-string prefixes, and engine-specific syntax tweaks.

    codegentargetsnippetcopy
    run · outputpreview · code
    const re = /…/
    snippet · livecode · ready
  4. 04

    Copy code

    One click copies the full snippet — paste into Node, a script, or your bundle.

    Copy writes via navigator.clipboard.writeText, so nothing transits the network and the output is byte-identical to what you see on screen.

    copyexportclipboardblob
    export · exportedready · saved
    Copied
    ready to shipsuccess
Pro tips

Regex patterns that don't melt down

Use named groups

(?<year>\d{4}) reads better than $1 and survives reordering. Supported in ECMAScript 2018+.

Anchor strictly

Use ^/$ with the m flag when matching whole lines. Without anchors, partial matches sneak through.

Avoid catastrophic backtracking

Nested quantifiers like (a+)+ can explode. Run patterns through ReDoS Detector first.

Escape every literal

Backslash any meta character you want literally: \.\$\^\*\+\?\(\)\[\]\{\}\|\\.

Test edge cases

Empty string, single character, unicode, the maximum length you expect — write fixtures for each.

Patterns aren&rsquo;t parsers

Don’t parse HTML, JSON, or balanced parens with regex. Use a proper parser when the grammar is recursive.

Related toolsRegex To PythonRegex To TypescriptRegex TesterRegex ExplainerRegex BuilderRegex Replace
Use Cases

When to generate JavaScript regex code

Skip the boilerplate when wiring a pattern into a Node service, browser app, or Deno script.

Form validation

Drop a generated test() call into a React/Vue input handler. Compiles through the JavaScript RegExp constructor — engine quirks (Unicode property escapes, sticky matching, named groups) work when their flags are on. Error messages cite the exact position of any syntax issue.

ReDoS-safe

Log parsing

Use matchAll to extract every line that matches a pattern. Pairs with the ReDoS detector to catch catastrophic backtracking before you deploy. A pattern that handles 1k-character input fine can become a denial-of-service vector on attacker-controlled 1M-character input.

ECMA-compliant

Search-and-replace

Run replace() in a build script to normalise text across files. Output exports as JavaScript, Python re, Java util.regex, .NET System.Text.RegularExpressions, PCRE, and POSIX — language quirks are highlighted on conversion so you don't ship a JS-only pattern to a Go service.

spec-grade

API filters

Sanitise inputs server-side with test() before they hit the DB. Capture groups (named or numbered) round-trip cleanly into replacement strings, JSON output, or CSV extraction without re-typing. Backreferences ($1, ${name}) preserve semantics across languages.

cross-engine

Live linting

Test patterns as the user types in an editor or terminal. Test against edge cases — empty input, single character, max length, multibyte boundaries — to catch off-by-one and zero-length match bugs before they reach production.

test-ready

Web Workers

Move heavy regex work off the main thread with the same snippet. All matching runs client-side so secret patterns never leave the browser. Useful when the pattern itself is sensitive (PII regexes, internal data formats, security filters).

production-ready
FAQ

Frequently asked questions

The /pattern/flags literal is more readable and compiled once. The RegExp constructor is the way to build a regex from a dynamic string at runtime — pass user input there, never the literal.
Inside the literal, write \b. Inside the constructor string, double it — "\\b" — because the string parser strips one layer before the regex parser sees it.
match returns the first match (or all matches if the g flag is set, without groups). matchAll requires the g flag and yields an iterator of full match objects with groups — what you usually want.
Yes. If the regex has captured groups, the matched separators end up in the result array alongside the surrounding fragments.
No. The code is generated entirely in your browser.
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