perf-regexes

Optimized and powerful regexes for JavaScript

Breaking Changes

In ES5, matching literal regexes with other regex in medium complexity code is highly risky.
In ES6 it is practically impossible.

For this reason, as of v1.0 JS_REGEX_P is deprecated and will be removed in the next minor version.

JS_REGEX will be maintained, but its use should be limited to complement other utilities, such as skip-regex, which uses a customized version of JS_REGEX to identify regular expresions reliably.

The minimum supported version of NodeJS now is 6.14 (oldest maintained LTS version w/fixes).

Install

npm install perf-regexes --save
# or
yarn add perf-regexes

In the browser, this loads perf-regexes in the global R object:

<script src="https://unpkg.com/perf-regexes/index.min.js"></script>

Included Regexes

All of these regexes recognize Win/Mac/Unix line-endings and are ready to be used, but you can customize them using the RegExp constructor and the source property of the desired regex.

HTML:

JavaScript:

Selection of lines:

NOTE

Because the 'g' flag, always set lastIndex or clone the regex before using it with the exec method.

Example

Using only one regex, this simple example will...

• Remove trailing whitespace of each line.
• Remove the empty lines.
• Normalize the line-endings to unix style.

const R = require('perf-regexes')

const cleaner = (text) => text.split(R.OPT_WS_EOL).filter(Boolean).join('\n')

console.dir(cleaner(' \r\r\n\nAA\t\t\t\r\n\rBB\nCC  \rDD  '))
// ⇒ 'AA\nBB\nCC\nDD'

Use the previous function to cleanup HTML text:

const htmlCleaner = (html) => cleaner(html.replace(R.HTML_CMNT, ''))

console.dir(htmlCleaner(
  '\r<!--header--><h1>A</h1>\r<div>B<br>\r\nC</div> <!--end-->\n'))
// ⇒ '<h1>A</h1>\n<div>B<br>\nC</div>'

Line-endings Normalization

const R = require('perf-regexes')

const normalize = (text) => text.split(R.EOL).join('\n')

console.dir(normalize('\rAA\r\r\nBB\r\nCC \nDD\r'))
// ⇒ '\nAA\n\nBB\nCC \nDD\n'

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
})

console.log(toSingleQuotes(`"A's" 'B' "C"`))
// ⇒ 'A\'s' 'B' 'C'

Matching Regexes

With the arrival of ES6TL and new keywords, finding literal regexes with another regex is not viable, you need a JS parser such as acorn or a specialized one such as skip-regex to do it correctly.

This is a very basic example that uses skip-regex:

import R from 'perf-regexes'
import skipRegex from 'skip-regex'

/**
 * Source to match quoted string, comments, and slashes.
 * Captures en $1 the slash
 */
const reStr = `${R.JS_STRING.source}|${R.JS_MLCMNT.source}|${R.JS_SLCMNT.source}|(/)`

/**
 * Search regexes in `code` and display the result to the console.
 */
const searchRegexes = (code) => {

  // Creating `re` here keeps its lastIndex private
  const re = RegExp(reStr, 'g')
  let match = re.exec(code)

  while (match) {
    if (match[1]) {
      const start = match.index
      const end = skipRegex(code, start)

      // skipRegex returns start+1 if this is not a regex
      if (end > start + 1) {
        console.log(`Found "${code.slice(start, end)}" at ${start}`)
      }
      re.lastIndex = end
    }
    match = re.exec(code)
  }
}

const code = `
const A = 2
const s = '/A/'            // must not find /A/

const re1 = /A/g           // regex
re1.lastIndex = 2 /A/ 1    // must not find /A/

/* /B/                     // must not find /B/
*/
const re2 = /B/g           // regex
re1.exec(s || "/B/")       // must not find /B/
`

searchRegexes(code)
// output:
// Found "/A/g" at 74
// Found "/B/b" at 210

The previous code does not support ES6TL, but it works quite well on ES5 files and is very fast.

For a more complete example of using perf-regexes, see js-cleanup, an advanced utility with support for ES6 that trims trailing spaces, compacts empty lines, normalizes line-endings, and removes comments conditionally.

ES6 Template Literals

ES6TLs are too complex to be identified by one single regex, do not even try.

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License

The MIT License (MIT)