Did this for SweetAlert.
npm install sweetalert --save
Add this to app.js:
require('sweetalert');
Then
npm run dev
It worked
[https://stackoverflow.com/questions/42512253/error-installing-sweetalert-on-laravel-through-npm]{https://stackoverflow.com/questions/42512253/error-installing-sweetalert-on-laravel-through-npm}