Is there a way detect if shelljs or node is installed in the system, within the script. I know it's kina dumb but, say in bash script it's possible to get the the $SHELL

Asking this because, say one decides to write a setup script with shelljs, then node becomes a dependency to get shelljs first....so bit confused... env['NODE_PATH'] would be useful? But also, can we know if shelljs is installed or not and then install it within shelljs 0_o