To install custom node modules, edit /app/data/env.sh using the File manager:
# note: this is a space separated list
export EXTRA_NODE_MODULES="handlebars@4.7.7 jsonata@2.0.2 marked@4.3.0"
The modules have to be whitelisted for use:
# note: this is a comma separated list
export NODE_FUNCTION_ALLOW_EXTERNAL=handlebars,jsonata,marked
Restart the app and use the module in Function nodes.
Restarting the app will install the modules specified in EXTRA_NODE_MODULES automatically.