This will not only empower devs build UWP apps but also test them with the Microsoft HoloLens or the Microsoft HoloLens Emulator available on the VS IDE.
What is HoloJS?
If you are a developer and feel interested in trying out the new tool, you should be running Visual Studio 2015 Update 3 to build.
To obtain information about the tools used for Windows Holographic development, including Microsoft Visual Studio 2015 Update 3 and the Microsoft HoloLens Emulator, go to Install the tools.
For instructions on how to developer unlock your Microsoft HoloLens, go to Enable your device for development.