This is what I had to do in order to get code completion for node.js to work with kdevelop on Ubuntu 14.04.
I have not run through these steps again on a fresh system so, I'm not sure if I'm missing anything here. If you find something missing please let me know.
#enable the backports repository to get kdevelop 4.7
sudo apt-add-repository ppa:kubuntu-ppa/backports
sudo apt-get update
#you may be able to skip this step if you want, but I did it.