Organising a project

🏠The everyday picture

A well-run office: departments by subject, a reception that directs visitors, and a manual on the front desk explaining where everything is.

📘What it really is

A typical small TypeScript project:

inventory/
  src/
    types.ts       shared types
    data.ts        sample or stored data
    inventory.ts   stock logic
    expenses.ts    expense logic
    utils.ts       small general helpers
    app.ts         starts the program
  tests/
    inventory.test.ts
  package.json
  tsconfig.json
  README.md
  .gitignore

Principles:
one subject per file: everything about expenses in expenses.ts;
logic separate from input and output: calculation files never print or save; app.ts does that (pure functions again, Module 23);
dependencies point one way: app.ts imports from the others, never the reverse;
names say what's inside, so you (and AI) can find things.
Tests can be written in TypeScript too: inventory.test.ts, run with node --test. Set "test" to node --test "tests/**/*.test.ts" in package.json.
package.json scripts become the project's controls: npm start, npm test, npm run check.
When working with AI on a project, tell it the structure and which file to change. Small, well-named files make AI's changes easier to check, one diff at a time (Builder Path, Lessons 4 and 5).

🖱️Try it

Reorganise your inventory project into the structure above. Add "start": "node src/app.ts" to the scripts, and move or write at least three tests into tests/. Check that npm start, npm test and npm run check all work.

✅Quick check

Why should calculation files never print or save?

Show the answer

Keeping logic pure makes it easy to test and reuse; input and output stay in one place.

inventory.ts imports from app.ts, and app.ts imports from inventory.ts. What's wrong?

Show the answer

A circular dependency. Dependencies should point one way, with app.ts at the top.