How to gracefully degrade reliance on shared scripts

[mike_nitobi]

I've written a suite of extensions for DW CS3 and I'm now working towards
supporting DW 8 (probably should have gone the other way...). I often make use
of the AssetInfo class defined in Shared/Common/Scripts/AssetInfoClass.js but
this class is absent from Dreamweaver 8.

So my question is this: what is the best way to conditionally include Shared
javascript files? I tried this:
var assetInfoClass = DWfile.read(dreamweaver.getConfigurationPath() +
"/Shared/Common/Scripts/AssetInfoClass.js");
eval(assetInfoClass);

but there must be scope issues because the AssetInfo class is available
sometimes and not others.