Of course you can use npm to download general JavaScript packages, and you can use them in the browser, if nothing, then manually.
The simplest use case:
npm install griddle-react --save
That installs the pacakge in node_modules/griddle-react folder.
From there you can simply include the script in your HTML:
<script src="node_modules/griddle-react/build/griddle.js">
But as Luiz has said,if you use something like browserify or webpack to also resolve the dependencies automatically, it gets even simple to use these things.