regexpu-core

6.4.0 verified Fri May 01 auth: no javascript

regexpu-core is the core module of regexpu, a transpiler that converts ES2015 Unicode regular expressions (with the `u` and `v` flags) into ES5-compatible patterns. Current stable version is 6.4.0. It supports features like Unicode property escapes, dotAll flag, named capture groups, and the `v` flag (unicodeSetsFlag), with options to either pass through or transform them. Released on npm with TypeScript types, it has a steady release cadence, updated for Unicode 15.1. Key differentiator: focused on core regexp rewriting without the full regexpu CLI, used by Babel and other tools.

Common errors

error TypeError: rewritePattern is not a function ↓

cause Using named import when default export expected in CJS.

fix

Use const rewritePattern = require('regexpu-core');

error Can't find module 'regexpu-core/data/character-class-escape-sets' ↓

cause Importing internal modules directly, not part of public API.

fix

Do not import from internal paths; use only 'regexpu-core'.

error TypeScript error: 'RewritePatternOptions' is a type and must be imported using a type-only import ↓

cause Using regular import for a type-only export.

fix

Use import type { RewritePatternOptions } from 'regexpu-core';

Warnings

breaking v6.0.0: Always enable unicodeSetsFlag parsing. Removed option to disable 'v' flag support. ↓

fix Remove any setting that disables 'v' flag; pattern is always parsed with 'v' flag support.

deprecated The 'useUnicodeFlag' option is deprecated since v5.0.0. ↓

fix Replace 'useUnicodeFlag' with 'unicodeFlag' option.

gotcha When using CommonJS require, the default export is the function, not an object. ↓

fix Use `const rewritePattern = require('regexpu-core');` not `require('...').rewritePattern`.

gotcha The 'unicodeFlag' option must be 'transform' to actually transform; false leaves it as-is. ↓

fix Set `unicodeFlag: 'transform'` explicitly to get ES5-compatible output.

gotcha Named capture groups are not transformed by default; must set 'namedGroups' option. ↓

fix Pass `namedGroups: 'transform'` option to compile named groups.

Install

npm install regexpu-core

yarn add regexpu-core

pnpm add regexpu-core

Imports

rewritePattern
wrong
```
const rewritePattern = require('regexpu-core')
```
correct
```
import rewritePattern from 'regexpu-core'
```
Default export; ESM and CJS both supported. In CJS, require returns the function directly.
rewritePattern (named)
wrong
```
import rewritePattern from 'regexpu-core'
```
correct
```
import { rewritePattern } from 'regexpu-core'
```
Named export also available since v5.1.0; both named and default exports are the same function.

types

wrong

import { RewritePatternOptions } from 'regexpu-core'

correct

import type { RewritePatternOptions } from 'regexpu-core'

Use `import type` for TypeScript interfaces to avoid runtime import.

Quickstart

Shows basic usage of rewritePattern to transpile a Unicode property escape regex into ES5-compatible pattern.

import rewritePattern from 'regexpu-core';

// Transform a Unicode regex with 'u' flag to ES5
const pattern = '\\p{ASCII_Hex_Digit}+';
const flags = 'u';
const result = rewritePattern(pattern, flags, {
  unicodePropertyEscapes: 'transform',
  unicodeFlag: 'transform',
});
console.log(result);
// E.g.: '(?:[0-9A-Fa-f])+'