// package.json
{
  // ...
  "scripts": {
    "build": "rollup -c",
    "dev": "rollup -c -w"
  }
}

// rollup.config.js
export default {
  entry: 'src/main.js',
  ...,
  watch: {
    chokidar: {
      // if the chokidar option is given, rollup-watch will
      // use it instead of fs.watch. You will need to install
      // chokidar separately.
      //
      // this options object is passed to chokidar. if you
      // don't have any options, just pass `chokidar: true`
    },
    // include and exclude govern which files to watch. by
    // default, all dependencies will be watched
    exclude: ['node_modules/**']
  }
};