concatRegexes

concatRegexes.js

const createConcatenator = escape => (...regexes) => {
  const join = regexes
    .map(x => (x instanceof RegExp ? regexToString(x) : escape(x)))
    .join("");

  const flags = regexes
    .map(x => x instanceof RegExp && x.flags)
    .filter(Boolean)
    .join("");

  const uniq = [...new Set(flags)].join("");
  return new RegExp(join, uniq);
};

export const concatRegexes = createConcatenator(escapeRegExp);
export const concatRegexesUnescaped = createConcatenator(String);

function regexToString(value) {
  return value.toString().replace(/^\/|\/[gi]*$/g, "");
}

// unused but can be useful
function stringToRegex(value, flags) {
  return new RegExp(escapeRegExp(value));
}

function escapeRegExp(value) {
  // $& means the whole matched string
  return value.replace(/[.*+?^${}()|[\]\\]/g, "\\$&").replace(/\n/g, "\\n");
}

concatRegexes.ts

const createConcatenator = (escape: (x: string) => string) => (
  ...regexes: (RegExp | string)[]
) => {
  const join = regexes
    .map(x => (x instanceof RegExp ? regexToString(x) : escape(x)))
    .join('');

  const flags = regexes
    .map(x => x instanceof RegExp && x.flags)
    .filter(Boolean)
    .join('');

  const uniq = [...new Set(flags)].join('');
  return new RegExp(join, uniq);
};

export const concatRegexes = createConcatenator(escapeRegExp);
export const concatRegexesUnescaped = createConcatenator(String);

function regexToString(value: RegExp) {
  return value.toString().replace(/^\/|\/[gi]*$/g, '');
}

// unused but can be useful
function stringToRegex(value: string, flags: string) {
  return new RegExp(escapeRegExp(value));
}

function escapeRegExp(value: string) {
  // $& means the whole matched string
  return value.replace(/[.*+?^${}()|[\]\\]/g, '\\$&').replace(/\n/g, '\\n');
}

usage.ts

import { concatRegexes } from './concatRegexes.ts'

const integer = /(\d+(?:,\d{3})*)/;

const myRegex = concatRegexes(
  /^Tu saldo es de €/,
  integer,
  '. Puedes retirar €', // dot is escaped
  integer,
  / hoy mismo (?<name>\w+)!$/
);

const match = 'Tu saldo es de €10. Puedes retirar €2 hoy mismo Matias!'.match(myRegex)
const saldo = match[1];
const puedoRetirar = match[2];
const nombre = match.groups.name;

console.log({ myRegex, saldo, puedoRetirar, nombre })

/*
Output:
{
  myRegex: /^Tu saldo es de €(\d+(?:,\d{3})*)\. Puedes retirar €(\d+(?:,\d{3})*) hoy mismo (?<name>\w+)!$/
  nombre: "Matias"
  puedoRetirar: "2"
  saldo: "10"
}
*/