regex-extract-loader

A webpack loader that uses regex to extract values from source files and make them available in code, or transform source into another form.

The regex-extract-loader takes a file's content as input, runs it against a user-supplied regular expression, and returns match information as its output by default. The output can be transformed, either on a per-match basis or at the end of the entire operation, using the match and/or project functions.

Example usage

Extract the attribute data from path tags in an svg file.

some.source.svg (input)

<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 3046.7 875.7">
  <title>webpack-logo</title>
  <path class="back" fill="#FFF" d="M387 0l387 218.9v437.9L387..."/>
  <path class="outer" fill="#8ED6FB" d="M704.9 641.7L399.8 814..."/>
  <path class="inner" fill="#1C78C0" d="M373 649.3L185.4 546...."/>
</svg>

webpack.config.js (config)

module.exports = {
  ...,
  module: {
    rules: [{
      test: /\.source.svg$/,
      use: {
        loader: 'regex-extract-loader',
        options: {
          regex: 'path.+\\bd="(.+?)"',  // can also be a RegExp object (required)
          flags: 'g'                    // ignored if a RegExp is used (optional)
          match: (match) => match,      // called for each match (optional)
          project: (result) => result   // called after processing (optional)
        }
      }
    }]
  }
}

some.module.js (output)

const pathData = require('./assets/some.source.svg')
 
  // Because the global flag was used, the result is an array of RegExp match objectss.
  [
    // First match
    [
      // 0: the entire match
      'path class="back" fill="#FFF" d="M387 0l387 218.9v437.9L387..."',
      // 1: the first (and only) capture group
      'M387 0l387 218.9v437.9L387...',
      // index: the index of the match in the input
      index: 101,
      // input: the entire input string
      input: '<svg xmlns="http://www.w3.org/2000/svg" viewBox=...>...</svg>'
    ],
    // Second match
    [
      'path class="outer" fill="#8ED6FB" d="M704.9 641.7L399.8 814..."',
      'M704.9 641.7L399.8 814...',
      index: 170,
      input: '<svg xmlns="http://www.w3.org/2000/svg" viewBox=...>...</svg>'
    ],
    // Third match
    [
      'path class="inner" fill="#1C78C0" d="M373 649.3L185.4 546...."',
      'M373 649.3L185.4 546....',
      index: 239,
      input: '<svg xmlns="http://www.w3.org/2000/svg" viewBox=...>...</svg>'
    ]
  ]

By default the entire match object is returned in the list, which includes the entire input. With the match and/or project options this can be pared down or transformed. See Using match and Using project below for details.

Typescript

Using import instead of require may cause issues when using Typescript to import text files. In this case, include a declarations.d.ts file in your project:

declarations.d.ts

declare module '*.svg' {
  const svg: any
  export default svg
}
 
declare module '*.txt' {
  const txt: any
  export default txt
}

Then you should be able to import the file:

import pathData from './source.svg'
import text from './somefile.txt'

Options object

options: {
  regex: 'path.+\\bd="(.+?)"',
  flags: 'g',
  match: (match) => match,
  project: (result) => result
}

regex (string|RegExp) (required) can be a string or RegExp object. For strings make sure escape characters use a double backslash, e.g., \\w+.

flags (string) (optional) used if regex is a string, otherwise ignored. If g (global) is specified either in the flags property or in the supplied regex, an array of RegExp match objects is returned. Otherwise a single RegExp match object is returned.

match (function) (optional) called for each match. Can be used to modify each match object. Must return a value if used.

project (function) (optional) called at the end of processing. Can be used to modify the final result. Must return a value if used.

Output: If the global flag g was used, the output will be a list of RegExp match objects. Otherwise it will be a single RegExp match object.

Using match

The match option can be used to modify the content of individual matches. A common use case is to return from the match object only items that would be needed in the final result. Since regex-extract-loader by default returns the RegExp match object, which includes the entire source string, it's much more efficient to only send along whatever is needed.

some.source.svg (input)

<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 3046.7 875.7">
  <title>webpack-logo</title>
  <path class="back" fill="#FFF" d="M387 0l387 218.9v437.9L387..."/>
  <path class="outer" fill="#8ED6FB" d="M704.9 641.7L399.8 814..."/>
  <path class="inner" fill="#1C78C0" d="M373 649.3L185.4 546...."/>
</svg>

webpack.config.js (config)

module.exports = {
  ...,
  module: {
    rules: [{
      test: /\.source.svg$/,
      use: {
        loader: 'regex-extract-loader',
        options: {
          regex: 'path.+\\bd="(.+?)"',
          flags: 'g'
          // Return the first (and only) caputre group
          match: (match) => match[1]
        }
      }
    }]
  }
}

some.module.js (output)

const pathData = require('./assets/some.source.svg')
 
  // The match function returned the first (and only) capture group,
  // so the final matches array contains only those items.
  [
    'M387 0l387 218.9v437.9L387...',
    'M704.9 641.7L399.8 814...',
    'M373 649.3L185.4 546....'
  ]

Using project

The project option can be used to modify the final result after all matches have been processed. It receives a list of items if the g (global) flag was specified in the regex, or a single item if g was not specified. The result passed to project will be whatever form was returned from match. If match is not used, the result passed to project will be either a list of RegExp match objects or a single one, depending on whether the regex was global or not.

some.source.svg (input)

<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 3046.7 875.7">
  <title>webpack-logo</title>
  <path class="back" fill="#FFF" d="M387 0l387 218.9v437.9L387..."/>
  <path class="outer" fill="#8ED6FB" d="M704.9 641.7L399.8 814..."/>
  <path class="inner" fill="#1C78C0" d="M373 649.3L185.4 546...."/>
</svg>

webpack.config.js (config)

module.exports = {
  ...,
  module: {
    rules: [{
      test: /\.source.svg$/,
      use: {
        loader: 'regex-extract-loader',
        options: {
          regex: 'path.+\\bd="(.+?)"',
          flags: 'g'
          // Transform each item in the match object into another form.
          project: (result) => {
            return result.map((match) => {
              return { path: match[1], index: match.index }
            })
          }
        }
      }
    }]
  }
}

some.module.js (output)

const pathData = require('./assets/some.source.svg')
 
  // The project function returned a list of custom objects.
  [
    { path: 'M387 0l387 218.9v437.9L387...', index: 101 },
    { path: 'M704.9 641.7L399.8 814...', index: 170 },
    { path: 'M373 649.3L185.4 546....', index: 239 }
  ]

Examples

Extract release information from a change log

changelog.md (input)

## [2.0.0] - 2017-11-20
New version

## [1.0.1] - 2017-11-07
Fix stuff

## [1.0.0] - 2017-11-05
Initial release

webpack.config.js (config)

module.exports = {
  ...,
  module: {
    rules: [{
      test: /changelog.md$/,
      use: {
        loader: 'regex-extract-loader',
        options: {
          regex: '\\s*## \\[(.+)\\] - (\\d{4}-\\d{2}-\\d{2})\n(.+)',
          flags: 'g',
          match: (match) => ({
            version: match[1], date: match[2], note: match[3]
          })
        }
      }
    }]
  }
}

some.module.js (output)

const versions = require('./changelog.md')
 
  [
    { version: '2.0.0', date: '2017-11-20', note: 'New version' },
    { version: '1.0.1', date: '2017-11-07', note: 'Fix stuff' },
    { version: '1.0.0', date: '2017-11-05', note: 'Initial release' }
  ]

Parse key/value pairs from a source in key=value format

some.source.cfg (input)

name=Nebula
rank=10
attributes=["female", "blue", "cybernetic", "angry", "nebulicious"]

webpack.config.js (config)

module.exports = {
  ...,
  module: {
    rules: [{
      test: /\.source.cfg$/,
      use: {
        loader: 'regex-extract-loader',
        options: {
          regex: '^(.+)=(.+)$',
          flags: 'mg',
          match: (match) => ({ key: match[1], value: match[2] }),
          project: (result) => {
            return result.reduce((map, item) => {
              try {
                map[item.key] = JSON.parse(item.value)
              } catch (e) {
                map[item.key] = item.value
              }
              return map
            }, {})
          }
        }
      }
    }]
  }
}

some.module.js (output)

const cfg = require('./assets/some.source.cfg')
 
{
  name: 'Nebula',
  rank: 10,
  attributes: [ 'female', 'blue', 'cybernetic', 'angry', 'nebulicious' ]
}

Other Examples

See the match and project unit tests for additional examples.