There are many ways to install Node, but for the latest version you cannot use apt install or apt-get install.
The best way is to use the Node Version Manager (nvm) to install Node.
Note that there is no Ubuntu package for nvm and nvm is not a regular binary, but rather a shell function.
Note also that nvm is not meant to be used with sudo ! The install will be for your current regular user.
Before installing: make sure to have a .bash_profile file in your home directory.
The following steps will install nvm and node (and hence npm).
curl -o- https://raw.githubusercontent.com/creationix/nvm/v0.33.8/install.sh | bash
Reload your terminal.
Find the latest version listed by the following command:
At the time of writing the latest was 9.5.0, so:
nvm install 9.5.0 nvm use 9.5.0
Check that the latest versions of node and npm are ready:
node -v npm -v