This is Tern. Tern is a stand-alone, editor-independent JavaScript analyzer that can be used to improve the JavaScript integration of existing editors.
Thanks to a group of generous crowd funders, Tern is open-source software, under an MIT license.
There are currently Emacs, Vim, Sublime Text, and Light Table plugins available, and built-in support in Brackets and Edge Code.
For further documentation, see the project page and the manual.