Webpack's `require.context` emulation for nodejs

1. Readme.md

Webpack's require.context is a powerful feature which helps to extract an array of paths within which the search of modules will be done. e.g.:

const requireFromContext = require.context(__dirname, true, /config\.js$/);
// Now `requireFromContext` contains files inside `__dirname/config` folder and which extension is `.js`

require.context is a special feature of webpack. Native nodejs's require doesn't containt that method and if you want to run unbundled code on nodejs, then you have to emulate require.context.

2. nodeRequireContext.js

const fs = require('fs');
const path = require('path');

/**
 * This function emulates behaviour of require.context
 * The reason why we can't return appropriate function in runtime is because require.context parses during build phase
 * Make sure that base is set relative to __dirname where it's called
 * @param base
 * @param scanSubDirectories
 * @param regularExpression
 * @returns {Module}
 */
require.context = (base = '.', scanSubDirectories = false, regularExpression = /\.js$/) => {
  const files = {};

  function readDirectory(directory) {
    fs.readdirSync(directory).forEach(file => {
      let fullPath = path.resolve(directory, file);

      if (fs.statSync(fullPath).isDirectory()) {
        if (scanSubDirectories) {
          readDirectory(fullPath);
        }

        return;
      }

      fullPath = fixWinPathSeparators(fullPath);

      if (!regularExpression.test(fullPath)) {
        return;
      }

      files[`./${fixWinPathSeparators(path.relative(base, fullPath))}`] = fullPath;
    });
  }

  readDirectory(path.resolve(__dirname, base));

  function Module(file) {
    try {
      // eslint-disable-next-line global-require
      return require(files[file]);
    } catch (err) {
      throw new Error(`
Can't resolve module ${file} from context ${JSON.stringify(files)}
Check if given context is correct: 
1. directory: ${path.resolve(__dirname, base)}
2. subDirectories: ${scanSubDirectories.toString()}
3. regularExpression: ${regularExpression}

Original message: ${err}
      `);
    }
  }

  Module.keys = () => Object.keys(files);

  return Module;
};

module.exports = require.context;

/**
 * Replaces win separators with unix-like
 * @param anyPath
 */
function fixWinPathSeparators(anyPath) {
  return anyPath.replace(/\\/g, '/');
}

3. example.js

// In case when you need to run application by node and your applications uses require.context webpack's feature, then this emulation will provide exactly the same bahevior
// I recommend to define an environment variable to determine how build is done, e.g. COMPILER

if (process.env.COMPILER === 'babel') {
  require.context = require('./nodeRequireContext');
} else {
  // Webpack's require.context will be used 
}

const requireFromContext = require.context(__dirname, true, /config\.js$/);

// ...