Read NodeJS internals first.
NPM does the needed graph de-duplications internally already when it generates the affective module layout in the file-system.
See npm dedupe docs.
Idea: Additional logic how module de-deduplication could be done will come to the conclusion that it is either invalid per definition, due to the previously described rules of graph/node identity that applies here, or that it is unnecessary, because it was already done by NPM.
This idea shall be falsified.
See Milestone: after-the-fact component deduplication
See Discussion: describe how component de-duplication works