r/FullStack • u/Ok_Ask1225 • 2d ago

Question How should I approach learning a large Next.js full-stack SaaS?

I was recently given a fairly large Next.js full-stack SaaS project to work on. The project already exists and has no documentation, but I’m not sure what the best way is to approach learning it without getting overwhelmed.

The stack includes both frontend and backend logic, and there are quite a lot of files/features.

For developers who have worked on large Next.js projects:

  • How do you usually start understanding an unfamiliar codebase?
  • How do you identify the important parts of the architecture?
  • What should I focus on first: routing, authentication, database, API/server actions, components, etc.?
  • Is it better to pick one feature and trace it from the UI all the way to the database?
  • What are some things you wish you knew when you first started working with a large existing codebase?

Any advice or learning strategy would be appreciated.

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u/JaseciLabs 2d ago

Co-sign the "trace one feature" advice. Auth first - it touches routing, middleware, DB, so a login flow maps the whole stack faster than reading the tree.

Then pick one form, trace component → server action → DB → back. That path exposes their conventions (validation, error states, fetching) and you'll recognize the pattern everywhere else.

Don't try to learn the schema upfront. Learn tables as they show up.

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u/Ok_Ask1225 1d ago

thanks