ua-optimized is an AMD plugin to enable branching to different built JavaScript layers with built-in known sets of features to create highly optimized applications created with feature detection. This allows one to write modules using feature detection and then uses UA sniffing only as a build-time optimization to determine features (the correct way to use UA sniffing, as it abstracts it away from correct code writing). To use ua-optimized, load your application entry point module using ua-optimized as a plugin:
require(["ua-optimized!my-app"]);