4.Find the Entry Point First

The Problem in Real Life

Reading Every File vs. Reading With One Question

Reading an Unfamiliar Codebase: Entry Point, Configuration, Endpoints, Database Access

• Read with a question: decide what you need to know before you open a file: "Where are sales numbers calculated?" "What happens when an organiser opens the dashboard?" Read only what answers it. Note other interesting things for later — and move on.
• Finding the entry point — the station: the entry point is where the program starts. Look at: the start script and main field in package.json, the Dockerfile's CMD, files named server.js, index.js, main.py, app.py, Main.java, Program.cs. In a web backend, the entry point usually creates the app, loads configuration, connects to the database, registers middleware and routes, and starts listening on a port (Act 19). It's the table of contents for the backend.
• Finding configuration: search for process.env (or os.environ, getenv) and the config folder. List every variable the code actually reads — that's the real list, whatever .env.sample says.
• Finding API endpoints and database access: from chapter two — routes via router definitions, database access via the query calls. For a feature, find the endpoint the frontend calls (search the frontend for fetch( or the URL) and follow it to the database.
• Navigate, don't scroll: use your editor's go to definition (jump to where a function is defined), find all references (everywhere it's used) and search across files. Follow the main road; skip the side streets.
• Read the history for the "why": git blame on a strange line shows who changed it and the commit message (Act 15), often linking an issue. git log -p path/to/file shows how a file evolved. Mark's "temporary fix for sales export" makes much more sense once you read the issue it links.
• Assume good reasons, check them: odd code often exists for a reason — a bug workaround, a customer requirement. Before "cleaning it up", find out why. If you can't, leave it, and write a note or ask.
• Keep notes and draw a map: as you go, write down what each part does (Act 24's notes habit) and sketch the main flow. Tomorrow-you, and the next person, will thank you.

const config = require("../config");          // 1. settings
const express = require("express");
const app = express();                         // 2. create the app

app.use(require("./middleware/logger"));       // 3. middleware
app.use(express.json());
app.use("/api", require("./routes"));          // 4. routes under /api
app.use(require("./middleware/errors"));       // 5. error handler

app.listen(config.port, () =>                  // 6. start listening
  console.log(`organiser-dashboard listening on ${config.port}`)
);