Codepen is the place where I go to boilerplate ideas quickly. It is usually the first place I go when I start a project or an idea. But, sometimes you want to hack with some NPM packages before you move them into your main projects for further development.
Unpkg is a CDN for all of the packages on NPM. Any easy way to access them is simply be referencing a file like this.
That will give you access to a certain file and a certain version that you are seeking out.
UNPKG has a ton of different options to references files and access them.
If you are using Codepen Projects, you can use a nodemodules folder and put your files inside of that. Then you can import them like normal in your other js files.