Which, in sample 2, I show can be assigned to any variable I like—I used $e for "enuff" in my first sample, then used $d3 in my second example, because, well, I'm Darby III. It's nice to be able to do this on the fly because if I was actually using D3.js in my project I could assign my own library to whatever other symbol I want.
Also in that second sample I set up the library file in a centrally located /assets/js/lib directory, under the v1 file name. Future additions to the library will be made to the file, until I hit a point when I want to refactor it or remove things from it, at which point I can tick over to a v2 file without breaking all my old samples.