Not sure when this started happening, but now my intellisense auto-completion is suggesting and using "Function (in DHtml.js, ...)" when I need it to be "function" while working in .js files.
How do I configure this option?
This appears to be fixed in the 8.2 EAP builds - http://youtrack.jetbrains.com/issue/RSRP-400812 (note that ticket says fixed in build 8.1.1000. That build isn't 8.1, and isn't available - it's been replaced by 8.2). Please can you try the EAP build and see if it fixes the problem? If not, please update the YouTrack ticket.
If you don't want to use the EAP build, I think you can work around the issue by clearing the solution's cache (ReSharper -> Options -> General -> Clear cache). As I understand it, the reason you're getting Function instead of function is due to ReSharper tracking selected items and giving previously selected items preference. Clearing the cache clears the tracked values and should allow you to use function again, but you might encounter the issue again at a later date.