I came across David Geary's article HTML5 2D game development: Implementing Sprite behaviors yesterday. The article ends with a download ZIP file.
I downloaded the ZIP, went to NetBeans IDE 7.3 Beta 2, and then chose File | New Project | HTML/JavaScript | HTML5 Application with Existing Sources. I then browsed to the root folder of the unzipped ZIP file and was then able to open it into the IDE. That makes understanding the source code and debugging it a lot easier because all the HTML5 capabilities of NetBeans IDE 7.3 are available to me immediately, e.g., Nashorn JavaScript editor, JavaScript debugger, bidirectional WebKit browser integration, HTML5 editor, CSS Rule Editor, etc:
Looking forward to following the rest of David Geary's series via NetBeans IDE.