webpacker.gemでapp/javascript/packs 以下にディレクトリを掘った場合に対応したconfig/webpack/shared.js

shared.js

var path = require('path')
var glob = require('glob')
var extname = require('path-complete-extname')

module.exports = {
  entry: glob.sync(path.join('..', 'app', 'javascript', 'packs', '**', '*.js*')).reduce(
    function(map, entry) {
      var relpath = path.relative(path.join('..', 'app', 'javascript', 'packs'), entry);

      var basename = path.basename(relpath, extname(relpath));
      var dirname = path.dirname(relpath);
      if(dirname != ".") {
        basename = path.join(dirname, basename)
      }

      map[basename] = entry
      return map
    }, {}
  ),

  output: { filename: '[name].js', path: path.resolve('..', 'public', 'packs') },

  module: {
    rules: [
      { test: /\.coffee(.erb)?$/, loader: "coffee-loader" },
      {
        test: /\.js(.erb)?$/,
        exclude: /node_modules/,
        loader: 'babel-loader',
        options: {
          presets: [
            [ 'latest', { 'es2015': { 'modules': false } } ]
          ]
        }
      },
      {
        test: /.erb$/,
        enforce: 'pre',
        exclude: /node_modules/,
        loader: 'rails-erb-loader',
        options: {
          runner: 'DISABLE_SPRING=1 ../bin/rails runner'
        }
      },
    ]
  },

  plugins: [],

  resolve: {
    extensions: [ '.js', '.coffee' ],
    modules: [
      path.resolve('../app/javascript'),
      path.resolve('../vendor/node_modules')
    ]
  },

  resolveLoader: {
    modules: [ path.resolve('../vendor/node_modules') ]
  }
}