https://github.com/rangoo94/find-regexp-beginning

Find character which could be on regexp beginning
https://github.com/rangoo94/find-regexp-beginning

analysis character parser regexp

Last synced: about 1 year ago
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Find character which could be on regexp beginning

• Host: GitHub
• URL: https://github.com/rangoo94/find-regexp-beginning
• Owner: rangoo94
• Created: 2018-02-13T16:02:54.000Z (over 8 years ago)
• Default Branch: master
• Last Pushed: 2018-02-13T16:11:30.000Z (over 8 years ago)
• Last Synced: 2025-03-02T06:18:52.219Z (over 1 year ago)
• Topics: analysis, character, parser, regexp
• Language: JavaScript
• Size: 36.1 KB
• Stars: 2
• Watchers: 2
• Forks: 0
• Open Issues: 0
• Metadata Files:
  • Readme: README.md

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README

          
# Find RegExp beginning

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[![NPM Downloads](https://img.shields.io/npm/dm/find-regexp-beginning.svg)](https://www.npmjs.com/package/find-regexp-beginning)

Useful, when you need to to detect what could be the first character which will pass regular expression (i.e. for lexer optimizations)

## How to install

Package is available as `find-regexp-beginning` in NPM, so you can use it in your project using

`npm install find-regexp-beginning` or `yarn add find-regexp-beginning`

## What are requirements?

Code itself is written in ES6 and should work in Node.js 4+ environment (best in Node.js 9+).

If you would like to use it in browser or older development, there is also transpiled and bundled (UMD) version included.

You can use `find-regexp-beginning/browser` in your requires or `FindRegexpBeginning` in global environment (in browser):

```js

// Load library

const findRegexpBeginning = require('find-regexp-beginning/browser')

const result = findRegexpBeginning(/abc/i) // [ 'a', 'A' ]

```

## How to use it?

Most importantly first argument is `RegExp` instance.

```js

const findRegexpBeginning = require('find-regexp-beginning')

const result1 = findRegexpBeginning(/abc/) // [ 'a' ]

const result2 = findRegexpBeginning(/abc/i) // [ 'a', 'A' ]

```

This function returns either list of possible characters on beginning

or `null` (when there is negation or any object is accepted).

Additionally, there is second argument `maxCharacters` (default: `15`).

It's important when you want to not detect characters if they exceed number of maximum characters,

i.e.:

```js

const findRegexpBeginning = require('find-regexp-beginning')

const result1 = findRegexpBeginning(/[1-9]/) // [ '1', '2', '3', '4', '5', '6', '7', '8', '9' ]

const result2 = findRegexpBeginning(/[1-9]/, 9) // [ '1', '2', '3', '4', '5', '6', '7', '8', '9' ]

const result3 = findRegexpBeginning(/[1-9]/, 100) // [ '1', '2', '3', '4', '5', '6', '7', '8', '9' ]

const result4 = findRegexpBeginning(/[1-9]/, Infinity) // [ '1', '2', '3', '4', '5', '6', '7', '8', '9' ]

const result5 = findRegexpBeginning(/[1-9]/, 3) // null

```