Vim Git Gutter (GitHub: airblade / vim-gitgutter, License: MIT) by Andrew Stewart shows a symbol in the sign column to indicate where lines have been added, modified, or deleted. This is based on Git Gutter for Sublime Text 2.
Vim's documentation in
:help sign-intro explains what the sign column is for if you're not familiar with it.
var fs = req
And then pressing
CTRL-X_CTRL-O will complete
var fs = require(
CTRL-X_CTRL-O again will display module name completion.