TS Regex Builder

A user-friendly regular expression builder 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 = 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 or a string.
• 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('abc')
• single element (string): 'Hello'
• array of elements: ['USD', oneOrMore(digit)]

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 API document.

Regex Builders

Builder	Regex Syntax	Description
buildRegExp(...)	/.../	Create RegExp instance
buildRegExp(..., { ignoreCase: true })	/.../i	Create RegExp instance with flags

Regex Constructs

Construct	Regex Syntax	Notes
capture(...)	(...)	Create a capture group
choiceOf(x, y, z)	x|y|z	Match one of provided sequences

Quantifiers

Quantifier	Regex Syntax	Description
zeroOrMore(x)	x*	Zero or more occurence of a pattern
oneOrMore(x)	x+	One or more occurence of a pattern
optional(x)	x?	Zero or one occurence of a pattern
repeat(x, n)	x{n}	Pattern repeats exact number of times
repeat(x, { min: n, })	x{n,}	Pattern repeats at least given number of times
repeat(x, { min: n, max: n2 })	x{n1,n2}	Pattern repeats between n1 and n2 number of times

Character classes

Character class	Regex Syntax	Description
any	.	Any character
word	\w	Word characters
digit	\d	Digit characters
whitespace	\s	Whitespace characters
anyOf('abc')	[abc]	Any of supplied characters
charRange('a', 'z')	[a-z]	Range of characters
charClass(...)	[...]	Concatenation of multiple character classes
inverted(...)	[^...]	Negation of a given character class

Anchors

Anchor	Regex Syntax	Description
startOfString	^	Match the start of the string (or the start of a line in multiline mode)
endOfString	$	Match the end of the string (or the end of a line in multiline mode)

Examples

See Examples document.

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
• Swift Regex Builder API docs
• Swift Evolution 351: Regex Builder DSL

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