Your First 24 Hours: Approaching a New Codebase

Walking into a 100,000-line codebase is like walking into a city for the first time. You don’t need to know every street; you just need to know the major landmarks.

Step 1: Run the App

Stop reading code! The first thing you should do is try to run the application locally.

1. Check README.md for setup steps.
2. Install dependencies (e.g., npm install, pip install -r requirements.txt).
3. Fix environment variables (e.g., .env.example -> .env).
4. Run it (npm start, python manage.py runserver).

Why? Understanding the app from a user’s perspective gives you a mental map of what the code is trying to do.

Step 2: Find the Entry Points

Every app starts somewhere.

• Frontend (Web): Look for index.html, main.ts, or App.tsx.
• Backend (API): Look for server.js, app.py, main.go, or routes/.
• CLI Tools: Look for main() or cmd/.

    App Entry Point (e.g., main.js)
        |
        +-- Configuration (env, DB setup)
        |
        +-- The Router (maps URLs to code)
              |
              +-- View/Controller (where the logic lives)

Step 3: Follow the “Golden Path”

Choose a simple feature, like a login or a button click, and follow it through the code.

1. Start at the UI: Find the code for that button.
2. Find the Event Handler: What happens when it’s clicked?
3. Trace the API Call: What URL does it hit?
4. Find the Backend Route: Where does that URL go in the server code?
5. See the Database Change: How is the data stored?

Practical Strategy: The “Read-Only” Day

For your first few hours, don’t try to change anything. Just browse.

• Open a file.
• Read the imports.
• Read the function names.
• Close the file.
• Repeat.

Mental Model: The Tourist

When you visit a new city, you don’t start by rebuilding the roads. You take a bus tour, look at the big buildings, and figure out where the grocery store is. Treat code the same way.

Common Mistake: “The Deep Dive Trap”

Don’t spend 2 hours reading a 500-line utility function for “formatting dates” on your first day. It’s just a helper. Focus on the core flow first.

Next: Understanding Project Structure