list and install npm packages before webpack build

InstallMissingModules.js

const thenify = require('thenify')
const webpack = require('webpack')
const MemoryFS = require('memory-fs')
const validateNpmPackageName = require('validate-npm-package-name')

class InstallMissingModules {
  constructor(options) {
    this.options = options
  }

  apply(compiler) {
    const runCompilerThenCallback = (...args) => {
      const callback = args[args.length - 1]
      this._runCompiler(compiler)
        .then(() => callback(), callback)
    };

    compiler.plugin(`run`, runCompilerThenCallback)
    compiler.plugin(`watch-run`, runCompilerThenCallback)
  }

  _runCompiler(compiler) {
    const { options } = compiler
    const { plugins } = options

    return this._findMissingModuleList(Object.assign({}, options, {
      plugins: plugins.filter(plugin => plugin.constructor !== InstallMissingModules)
    }))
    .then(list => this.options.callback(list))
  }

  _findMissingModuleList(webpackConfig) {
    const webpackCompiler = webpack(webpackConfig)
    webpackCompiler.outputFileSystem = new MemoryFS()
    return new Promise((resolve, reject) => {
      webpackCompiler.run((error, stats) => {
        const { errors }  = stats.toJson()

        const list = errors.map(error => {
          if (/Module not found: Error: Cannot resolve module '(\S+)' in/.test(error)) {
            return RegExp.$1
          } else if (/Cannot find module '(\S+)'/.test(error)) {
            return RegExp.$1
          } else {
            return undefined
          }
        })
        .filter(it => !!it)
        .map(it => it.split('/')[0])
        .filter(it => validateNpmPackageName(it).validForNewPackages)

        resolve(list)
      })
    })
  }
}

module.exports = InstallMissingModules