perf-regexes

Optimized and powerful regexes for JavaScript

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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

``sh
npm install perf-regexes --save


or

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

`html

`

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:

Name | Flags | Matches
---------- | :---: | -------
HTML_CMNT | g | Valid HTML comments, according to the SGML standard.

JavaScript:

Name | Flags | Matches
---------- | :---: | -------
JS_MLCMNT | g | Multiline JS comment, with support for embedded '/*' sequences.
JS_SLCMNT | g | Single-line JS comments, not including its line-ending.
JS_DQSTR | g | Double quoted JS string, with support for escaped quotes and line-endings.
JS_SQSTR | g | Single quoted JS string, with support for escaped quotes and line-endings.
JS_STRING | g | Combines JS_SQSTR and JS_DQSTR to match single or double quoted strings.
JS_REGEX | g | Regex. Note: The result must be validated.
JS_REGEX_P | g | _Deprecated, do not use it._

Selection of lines:

Name | Flags | Matches
--------------- | :---: | -------
EMPTY_LINES | gm | Empty line or line with only whitespace within, including its line-ending, if it has one.
NON_EMPTY_LINES | gm | Line with at least one non-whitespace character, including its line-ending, if it has one.
TRAILING_WS | gm | The trailing whitespace of a line, without including its line-ending.
OPT_WS_EOL | g | Zero or more blank characters followed by a line-ending, or the final blanks, if the (last) line has no line-ending.
EOL | g | Line-ending of any type

$3

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.

`js
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:

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

console.dir(htmlCleaner(
'\r

A

`js
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'
`

$3

`js
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'
`

$3

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:

`js
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.

$3

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

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License

The MIT License (MIT)

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