Make sure node.js v6 is installed from nodesource.

Install Node.js

Just like a fresh new installation.

List current env:

$ node -v
v6.10.3
$ npm -v
3.10.10
$ cat /etc/apt/sources.list.d/nodesource.list
deb https://deb.nodesource.com/node_6.x xenial main
deb-src https://deb.nodesource.com/node_6.x xenial main

Setup apt source:

curl -sL https://deb.nodesource.com/setup_8.x | sudo -E bash -

Check apt source:

$ cat /etc/apt/sources.list.d/nodesource.list
deb https://deb.nodesource.com/node_8.x xenial main
deb-src https://deb.nodesource.com/node_8.x xenial main

Begin to install nodejs package:

sudo apt-get install -y nodejs

After installtion, check version of node.js:

$ node -v
v8.1.4
$ npm -v
5.0.3

Upgrade NPM

sudo npm i -g npm

$ npm -v
5.3.0

Leftover

cd into node.js project and rebuild all you native(C++) addons/packages.

npm rebuild

Note for upgrading Node.js:

Sometimes new version of Node.js is shipping with a new version of V8, existing native addons will need to be recompiled or runtime errors will occur when trying to load them. Use npm rebuild or simply remove your node_modules dir and npm install from scratch.