npm install --save extra-watch-webpack-plugin

• files: string (absolute path or glob pattern) or array, default [], attach extra files to webpack's watch system
• dirs: string or array, default [], attach extra dirs to webpack's watch system

// webpack.config.js
import ExtraWatchWebpackPlugin from 'extra-watch-webpack-plugin';
......
{
  plugins: [
    new ExtraWatchWebpackPlugin({
      files: [ 'path/to/file', 'src/**/*.json' ],
      dirs: [ 'path/to/dir' ],
    }),
  ],
}