TS Regex Builder

Build maintainable regular expressions for TypeScript and JavaScript.

API docs | Examples

Goal

Regular expressions are a powerful tool for matching text patterns, yet they are notorious for their hard-to-parse syntax, especially in the case of more complex patterns.

This library allows users to create regular expressions in a structured way, making them easy to write and review. It provides a domain-specific langauge for defining regular expressions, which are finally turned into JavaScript-native RegExp objects for fast execution.

// Regular JS RegExp
const hexColor = /^#?([a-fA-F0-9]{6}|[a-fA-F0-9]{3})$/;

// TS Regex Builder DSL
const hexDigit = /[a-fA-F0-9]/; // or: charClass(charRange('a', 'f'), charRange('A', 'F'), charRange('0', '9'));

const hexColor = buildRegExp([
  startOfString,
  optional('#'),
  capture(
    choiceOf(
      repeat(hexDigit, 6), // #rrggbb
      repeat(hexDigit, 3), // #rgb
    ),
  ),
  endOfString,
]);

Installation

npm install ts-regex-builder

or

yarn add ts-regex-builder

Basic usage

import { buildRegExp, capture, oneOrMore } from 'ts-regex-builder';

// /Hello (\w+)/
const regex = buildRegExp(['Hello ', capture(oneOrMore(word))]);

Regex domain-specific language

TS Regex Builder allows you to build complex regular expressions using domain-specific language.

Terminology:

• regex construct (RegexConstruct) - common name for all regex constructs like character classes, quantifiers, and anchors.
• regex element (RegexElement) - a fundamental building block of a regular expression, defined as either a regex construct, a string, or RegExp literal (/.../).
• regex sequence (RegexSequence) - a sequence of regex elements forming a regular expression. For developer convenience, it also accepts a single element instead of an array.

Most of the regex constructs accept a regex sequence as their argument.

Examples of sequences:

• single element (construct): capture('Hello')
• single element (string): 'Hello'
• single element (RegExp literal): /Hello/
• array of elements: ['USD', oneOrMore(digit), /Hello/]

Regex constructs can be composed into a tree structure:

const currencyCode = repeat(charRange('A', 'Z'), 3);
const currencyAmount = buildRegExp([
  choiceOf('$', '€', currencyCode), // currency
  capture(
    oneOrMore(digit), // integer part
    optional(['.', repeat(digit, 2)]), // fractional part
  ),
]);

See Types API doc for more info.

Regex Builders

See Builder API doc for more info.

Regex Constructs

See Constructs API doc for more info.

> [!NOTE] > TS Regex Builder does not have a construct for non-capturing groups. Such groups are implicitly added when required.

Quantifiers

See Quantifiers API doc for more info.

Assertions

See Character Classes API doc and Unicode API doc for more info.

Examples

See Examples.

Performance

Regular expressions created with this library are executed at runtime, so you should avoid creating them in a context where they would need to be executed multiple times, e.g., inside loops or functions. We recommend that you create a top-level object for each required regex.

Contributing

See the contributing guide to learn how to contribute to the repository and the development workflow. See the project guidelines to understand our core principles.

License

MIT

Inspiration

TS Regex Builder is inspired by Swift Regex Builder API.

Reference

• ECMAScript Regular Expression BNF Grammar
• Unicode Regular Expressions
• Swift Evolution 351: Regex Builder DSL
• Swift Regex Builder API docs

Made with create-react-native-library