Usually we run : 

npm start

to start an app, then we we might call other script to do something:

npm build && nodemon app

 

Actaully we can use "prestart" to simpify this, because npm will check if there is "prestart" script, if there is it will run prestart before start:

"prestart": "babel src --out-dir dist","start": "node dist/index.js"