The way pnathan described his app, systemXHR doesn't seem to make sense for it. You usually only need systemXHR when you are writing an app that talks to a third-party server that you cannot control and that you cannot convince to enable CORS. systemXHR also has different handling of cookies and HTTP authentication credentials.

Yes, but you cannot load external scripts. Only content or XHR. I thought the OP was talking about loading code over the network.