NPM is the NodeJS package manager. It works well enough that it's used for all sorts of packaging, even when NodeJS isn't involved.
To install dygraphs via NPM, simply run:
npm install dygraphs
This will install dygraphs under a node_modules directory, for example:
Once you've got it installed, you can source it from that location in your web page, web server, Python program, whatever.
ls -lh node_modules/dygraphs/dygraph-combined.js
If you create a package.json file, you can specify a specific version of dygraphs that you'd like to depend on. That way, you can keep getting a compatible version in the 1.x series, even after we move on to 2.x.