Use the npm client without Node.js application

Simply use the full path

npm
/opt/alt/alt-nodejs8/root/usr/bin/npm

node

/opt/alt/alt-nodejs8/root/usr/bin/node

Optionally, add npm and node aliases to avoid using the full path:

nano ~/.bash_profile

ADD

alias npm="/opt/alt/alt-nodejs8/root/usr/bin/npm"
alias node="/opt/alt/alt-nodejs8/root/usr/bin/node"