ReRE.js

Re-implementation of ECMA-262 (JavaScript) RegExp.

About

ReRE.js is a framework for processing ECMA-262 (JavaScript standard) RegExp. It provides:

• parser which constructs AST nodes from a RegExp pattern string,
• engine which executes RegExp matching against an input string, and
• ponyfill (or shim) which is complete and full-featured alternative of RegExp class.

ReRE.js supports the latest RegExp features:

• look-behind assertion ((?<=...)),
• named capture group, named back reference ((?<foo>...) and \k<foo>), and
• Unicode property class (\p{ASCII}).

Moreover, ReRE.js supports "Additional ECMAScript Features for Web Browsers" for RegExp. It means robust, so it can parse some terrible real-world RegExp patterns correctly.

Getting Started

Install ReRE.js as dependency:

$ npm install rerejs

Then, you can start:

import {
  // A parser for `RegExp` pattern.
  Parser,
  // A compiler for parsed `RegExp` pattern node.
  Compiler,
  // A ponyfill of `RegExp`.
  RegExpCompat
} from './index';

/*
 * Usage of `Parser`.
 */

// `new Parser` with parsing pattern source and flags,
// then call `parse` method to execute parsing.
const parser = new Parser('a+', 'u');
const pattern = parser.parse();

console.log(pattern);
// => {
//     type: 'Pattern',
//     flagSet: {
//       global: false,
//       ignoreCase: false,
//       multiline: false,
//       unicode: true,
//       dotAll: false,
//       sticky: false
//     },
//     captureParens: 0,
//     names: Map(0) {},
//     child: {
//       type: 'Some',
//       nonGreedy: false,
//       child: { type: 'Char', value: 97, raw: 'a', range: [ 0, 1 ] },
//       range: [ 0, 2 ]
//     },
//     range: [ 0, 2 ]
//   }

/*
 * Usage of `Compiler`.
 */

// `new Compiler` with pattern node, then call `compile` to get `program`.
const compiler = new Compiler(pattern);
const program = compiler.compile();

// `program` is compiled regular expression pattern.
// To execute matching, invoke `exec` method.
// Note that `program` is not `RegExpCompat` instance,
// and `exec` method result is not the same as `RegExp.prototype.exec`.
console.log(program.exec('bbaaabb'));
// => Match [
//      0 [0:0] => '',
//    ]

/*
 * Usage of `RegExpCompat`.
 */

// You cau use `RegExpCompat` like `RegExp` very.
const re = new RegExpCompat('a+', 'u');

console.log(re.exec('bbaaabb'));
// => [ 'aaa', index: 2, input: 'bbaaabb', groups: undefined ]

// Also, you can pass `RegExpCompat` instance to
// `String.prototype.match`, `String.prototype.replace`
// and other methods accepts `RegExp` instance.
console.log('bbaaabb'.match(re));
// => [ 'aaa', index: 2, input: 'bbaaabb', groups: undefined ]
console.log('bbaaabb'.replace(re, 'ccc'));
// => bbcccbb

// You can write `global.RegExp = RegExpCompat;`,
// however it does not work as you expected because
// it does not override `RegExp` literals construction.

Contributing

ReRE.js is alpha quality project for now, so there are many bugs and problems. If you found something, please open an issue.

Especially such reports are needed:

• "There is a different behavior between the browser and ReRE.js."
• "RegExp matching goes on infinite-loop. VM Bug?"
• "A typo in comment or error message is found."

Pull Requests are also welcome.

However I concentrate improving ReRE.js ECMA-262 compatibility for now. So, I cannot accept a feature request as soon. Notably, it is out of targets of this project that extending RegExp syntax. (e.g. support x flag like Perl regular expression)

Documents for Developer

There are few documents for now. Sorry.

• docs/canonicalize.md: the explanation of src/canonicalize.ts.
• docs/vm.md: the explanation for the VM using ReRE.js on matching.

License

ReRE.js is licensed under MIT license.

(C) 2020-2022 TSUYUSATO "MakeNowJust" Kitsune