regexpu

4.8.0 verified Fri May 01 auth: no javascript

regexpu is a source code transpiler that enables the use of ES2015 Unicode regular expressions (the `u` flag) in ES5 environments. It rewrites regex literals with the `u` flag into equivalent ES5-compatible patterns, handling Unicode properties, escapes, and case folding. Current version 4.8.0 (stable) releases infrequently; major version bumps (e.g., 2.0.0) introduced breaking changes in module export paths. Key differentiators: it is the core engine behind Babel, Traceur, and other transpilers for Unicode regex; also ships `regexpu-core` for programmatic use. Supports Node >=6 and browsers via bundlers.

Common errors

error require is not defined ↓

cause Trying to use CommonJS require in an ESM module (e.g., .mjs file or type:module).

fix

Use import statements: import { rewritePattern } from 'regexpu-core';

error Cannot find module 'regexpu' or 'regexpu-core' ↓

cause Module not installed or incorrect import path.

fix

Install the correct package: npm install regexpu --save (or regexpu-core if using core).

error rewritePattern is not a function ↓

cause Import destructuring error; default export vs named export confusion.

fix

Use named import: import { rewritePattern } from 'regexpu-core';

Warnings

breaking Breaking change in v2.0.0: require('regexpu-core') is the new require('regexpu/rewrite-pattern') ↓

fix Update imports: use require('regexpu-core') or import { rewritePattern } from 'regexpu-core' instead of old require('regexpu').rewritePattern.

deprecated Using require('regexpu') directly may be deprecated; prefer regexpu-core submodule. ↓

fix Switch to require('regexpu-core') for the rewritePattern function.

gotcha The package only transpiles the regex pattern string; it does not handle the regular expression literal syntax. Pass the pattern without delimiters. ↓

fix Ensure input is a string pattern (e.g., '\\p{ASCII_Hex_Digit}') not '/\\p{ASCII_Hex_Digit}/u'.

gotcha Options object must be passed correctly: { unicodePropertyEscape: true } to enable Unicode property escapes (default false). ↓

fix Pass options as second or third argument to rewritePattern.

Install

npm install regexpu

yarn add regexpu

pnpm add regexpu

Imports

rewritePattern
wrong
```
const rewritePattern = require('regexpu').rewritePattern
```
correct
```
import { rewritePattern } from 'regexpu'
```
Before v2.0.0, the correct import was require('regexpu').rewritePattern; after v2.0.0, ESM-style named import is preferred. CommonJS users should use the new path.
default
wrong
```
const regexpu = require('regexpu')
```
correct
```
import regexpu from 'regexpu'
```
Default export exists in ESM; CommonJS requires destructuring. ESM-only since v2.0.0?
rewritePattern (from regexpu-core)
wrong
```
const rewritePattern = require('regexpu').rewritePattern
```
correct
```
import { rewritePattern } from 'regexpu-core'
```
The core module regexpu-core is the recommended way since v2.0.0; the main package now re-exports it.

Quickstart

Transpiles a Unicode regex pattern with the u flag to an ES5-compatible equivalent, demonstrating usage of rewritePattern with options.

import { rewritePattern } from 'regexpu-core';

// Transpile a regex with the u flag to ES5
const pattern = '\\p{ASCII_Hex_Digit}';
const flags = 'u';
const result = rewritePattern(pattern, flags);
console.log(result); // '[A-Fa-f0-9]'

// With support for Unicode properties
const pattern2 = '\\p{Emoji}';
const flags2 = 'u';
const result2 = rewritePattern(pattern2, flags2, { unicodePropertyEscape: true });
console.log(result2); // '[...]'