On launching the file, they declare those Global fields to Global Variables
Then in the web viewer they use the data:text/html approach, pulling everything into the Web Viewer directly from FileMaker — there is no need to reference any external files. In particular here, they are referencing the .js global variables they created on startup.
The result is a set of very sweet looking graphs with a bit of interactivity or animation and zero footprint on your hard drive. Everything generated comes from elements within FileMaker. I like this approach. It appears that it would be very straight forward to implement. I especially like the chart that handles a large number of data points. I haven’t tried charting with FileMaker 12 yet, but previous versions are a bit lacking with large data sets. This demo is well worth downloading from Logicurio and examining.