I'm working on a Windows Store App (JavaScript/HTML/CSS) that will be deployed directly to devices in our enterprise.
I want to keep the datasources (urls to Restful web APIs) as part of the configuration rather than built into the app itself so that I can set them during deployment (e.g. to set test urls and prod urls).
More generally I want to store text variables in config that is external to the app and can be pulled in by the app somehow.
I thought I could set some environment variables or something but Windows Store Apps can't read them it seems.
Any ideas?
You could certainly make an HTTP request from the app on startup to retrieve a configuration file, but that of course assumes connectivity which may or may not work in your scenario. For a Store-acquired app, this is really the only choice.
In your scenario, however, you'll be doing side-loading through a Powershell, correct? (This is implied in installing directly to devices.) In that case, the Powershell script is running in full trust and will have access to the file system during the process. This means that the script can easily deploy a configuration file into the app's local appdata folder, which the app then picks up when it runs. The app package should also contain a default configuration file that it copies into that appdata folder if such a file doesn't exist on startup.
The documentation for the add-appxpackage script that does the install is here: https://technet.microsoft.com/en-us/library/hh856048.aspx.
Another option you might be able to use is to build different versions of your packages for test and production deployment. It is possible to configure the build process in Visual Studio to selectively bring in different versions of a file depending on your build target (e.g. Debug or Release). I have a blog that describes this technique on http://www.kraigbrockschmidt.com/2014/02/25/differentiate-debug-release-builds-javascript/. This would allow you to package different versions of a configuration file into the package, which you'd then read from the package install location at runtime or copy to appdata if you wanted to make changes at runtime.
I mention this method for building different packages because it's something that doesn't need you to do anything other than change the build target. It accomplishes what you would do with #ifdef precompiler directives in other languages, which aren't available for JavaScript.