Optimized Regular Expressions for JavaScript

Common errors

• TypeError: R.JS_REGEX_P is not a function (or similar 'undefined' error)

  cause Attempting to use the deprecated `JS_REGEX_P` regex, which has been removed or is no longer accessible.
  fix Replace `R.JS_REGEX_P` with `R.JS_REGEX` and implement additional validation, or consider using alternative parsing strategies.

• Unexpected empty matches or incorrect parsing when repeatedly calling 'exec()' on a global regex.

  cause The `lastIndex` property of a global regex (`g` flag) was not reset between calls to `exec()`, causing it to resume from the previous match's end.
  fix Set `yourRegex.lastIndex = 0;` before each new `exec()` call on the same regex instance, or create a new `RegExp` instance each time.

• ReferenceError: R is not defined

  cause The `perf-regexes` library's default export `R` was not correctly imported or required in a module environment, or the UMD bundle was not loaded in the browser.
  fix In CommonJS, use `const R = require('perf-regexes');`. For ESM, use `import R from 'perf-regexes';`. In a browser, ensure `<script src="https://unpkg.com/perf-regexes/index.min.js"></script>` is loaded before attempting to access `window.R`.

Warnings

• deprecated `JS_REGEX_P` is deprecated as of v1.0 and will be removed in a future minor version. It is highly risky to match literal regexes with other regexes, especially in ES6+ environments.
  Fix: Avoid using `JS_REGEX_P`. If you need to identify regexes, use `JS_REGEX` and perform additional validation or consider dedicated parsing libraries.
• gotcha When using any regex with the global (`'g'`) flag, you must manually reset `lastIndex` before each new `exec` call or clone the regex instance to prevent unexpected behavior and incorrect matches.
  Fix: Before each `regex.exec(text)` call, ensure `regex.lastIndex = 0;` or create a new regex instance, e.g., `const newRegex = new RegExp(R.YOUR_REGEX.source, R.YOUR_REGEX.flags);`.
• breaking The minimum supported version of NodeJS is now 6.14. Running on older versions may lead to compatibility issues or errors.
  Fix: Ensure your Node.js environment is version 6.14 or higher. Update Node.js if necessary.
• gotcha The `JS_REGEX` pattern should be used with caution and its results validated. Matching complex JavaScript regexes reliably with simple regex patterns is inherently difficult and prone to edge cases.
  Fix: Limit the use of `JS_REGEX` to complement other utilities or for less critical parsing tasks. For robust JavaScript parsing, consider a dedicated AST parser or a more sophisticated tokenization library.

Install

• npm install perf-regexes npm
• yarn add perf-regexes yarn
• pnpm add perf-regexes pnpm

Imports

• R
  wrong:

  import { R } from 'perf-regexes';

  correct:

  import R from 'perf-regexes';

  `R` is the default export containing all regex patterns as properties. For CommonJS, use `const R = require('perf-regexes');`. In browsers, it's available as `window.R` if loaded via UMD.
• HTML_CMNT
  wrong:

  import { HTML_CMNT } from 'perf-regexes';

  correct:

  import R from 'perf-regexes';
  const htmlCommentRegex = R.HTML_CMNT;

  Individual regexes like `HTML_CMNT` are properties of the default `R` object, not named exports.
• JS_STRING
  wrong:

  import { JS_STRING } from 'perf-regexes';

  correct:

  import R from 'perf-regexes';
  const jsStringRegex = R.JS_STRING;

  Regexes are accessed as properties of the default `R` object. This pattern combines `JS_SQSTR` and `JS_DQSTR` for convenience.
• JS_REGEX_P
  wrong:

  import { JS_REGEX_P } from 'perf-regexes';

  correct:

  import R from 'perf-regexes';
  const deprecatedRegex = R.JS_REGEX_P;

  This regex is deprecated as of v1.0 and is slated for removal in future versions due to inherent risks in matching literal regexes. Prefer `JS_REGEX` with additional validation.

Quickstart

This quickstart demonstrates how to use `perf-regexes` to clean text by removing empty lines and trailing whitespace, normalize HTML by stripping comments, and convert double-quoted JavaScript strings to single-quoted strings.

const R = require('perf-regexes');

// Function to remove trailing whitespace, empty lines, and normalize line-endings
const cleaner = (text) => text.split(R.OPT_WS_EOL).filter(Boolean).join('\n');

console.log('Cleaned text example:');
console.dir(cleaner(' \r\r\n\nAA\t\t\t\r\n\rBB\nCC  \rDD  '));
// Expected output: 'AA\nBB\nCC\nDD'

// Use the cleaner function to cleanup HTML text by first removing HTML comments
const htmlCleaner = (html) => cleaner(html.replace(R.HTML_CMNT, ''));

const rawHtml = '\r<!--header--><h1>A</h1>\r<div>B<br>\r\nC</div> <!--end-->\n';
console.log('\nCleaned HTML example:');
console.dir(htmlCleaner(rawHtml));
// Expected output: '<h1>A</h1>\n<div>B<br>\nC</div>'

// Demonstrating string conversion: Double-quoted to single-quoted strings
const toSingleQuotes = (text) => text.replace(R.JS_STRING, (str) => {
  return str[0] === '"'
    ? `'${str.slice(1, -1).replace(/'/g, "\'")}'`
    : str;
});

const stringWithQuotes = `"A's" 'B' "C" "D\\"E" 'F\\\'G'`;
console.log('\nString quote conversion example:');
console.log(toSingleQuotes(stringWithQuotes));
// Expected output: 'A\'s' 'B' 'C' 'D\"E' 'F\'G'