Rare Regex Utils

Zero-dependency TypeScript library for rare regex utilities:

Install

npm install rare-regex-utils

TODO: how to import TypeScript sources vs. JavaScript bundle.

Limitations

• Not full regex syntax supported (yet)
• Some functions have worst case exponential complexity. Usually just pathological cases. Please report.

Documentation

intersection(re1: RegExp, re1: RegExp): RegExp

import { intersection } from 'regex-utils'

// password constraints as 
const constraints = [
  /.{12,}/,  // min length 12 letters
  /[0-9]/,   // at least one number
  /[A-Z]/,   // at least one upper case letter   
  /[a-z]/,   // at least one lower case letter
]

// Combine into a single regex:
const passwordRegex = constraints.reduce(intersection)

complement(re: RegExp): RegExp

enumerate(re: RegExp): RegExp

derivative(re: RegExp): RegExp

Todo Utilities

• recognize regex prone to catastrophic backtracking
  • https://www.regular-expressions.info/catastrophic.html
  • https://www.youtube.com/watch?v=DDe-S3uef2w
• check equivalence of two regex or find counterexample string

References

Heavily informed by this paper: https://www.khoury.northeastern.edu/home/turon/re-deriv.pdf