Watch changes while developing a NPM package

1. Install https://www.npmjs.com/package/npm-watch

2. Add this to packages json

"watch": {
  "build-my-app": {
    "patterns": [
      "src"
],
    "extensions": "js,vue"
}
},
"scripts": {
  "build": "rollup -c",
  "build-my-app": "npm run build",
  "watch": "npm-watch"
},

3. Start watching with

npm run watch