One thing to consider is that while adding the repository using $(lsb_release -sc) works in ubuntu, it may not work on Ubuntu based distributions such as Linux Mint. The script from nodesource does a translation from the Ubuntu based distribution name to the corresponding Ubuntu distribution name.
For example: "Linux Mint" "sylvia" is mapped to "Ubuntu" "xenial"
Which means that if you want to use the instructions as shown in the response in an Ubuntu based distribution, you need to replace $(lsb_release -sc) with the actual base Ubuntu distribution.
For example, to install in Linux Mint sylvia, you need to enter
sudo apt-add-repository "deb https://deb.nodesource.com/node_7.x xenial main"