Avoid external npm package to reinstall at each start

Hi,

It's more a question than an issue : i searched on issue and doc but i had no found how install npm package.

var pack = require('npmPack') install correctly module and depencies but with no persistance.
Each time i start the fiddle the package seems to be reisntall (in the console i got : Installing node modules using npm: npmPack)

It's normal or there are a way to persist npm module ?

Thanks