How I Spot a Copy-Pasted React Developer Project in Minutes

# Commits in order, with files changed
git log --reverse --stat --oneline | head -40

# How many commits, over how many days
git log --format=%ad --date=short | sort -u | wc -l

# Which packages are listed but never imported?
npx depcheck

# Find leftover starter files
git ls-files | grep -Ei "logo|serviceWorker|reportWebVitals"

a1c3e2f Set up Vite + React, add ESLint
4b7d901 Add product list with mock data
9e2a114 Fetch products from API, add loading state
c81f0aa Add cart reducer: add, remove, quantity
2d4e7b3 Fix: quantity could go below 1
7f90c12 Persist cart to localStorage
0aa3b6d Add tests for cart reducer
5c2e8d1 Make cart drawer keyboard accessible

Small steps, real fixes, a test commit.
This history tells me someone actually built it.

export const initialCart = { items: [] };

export function cartReducer(state, action) {
  switch (action.type) {
    case "add": {
      const found = state.items.find((i) => i.id === action.item.id);
      if (found) {
        return {
          items: state.items.map((i) =>
            i.id === action.item.id ? { ...i, qty: i.qty + 1 } : i
          ),
        };
      }
      return { items: [...state.items, { ...action.item, qty: 1 }] };
    }
    case "setQty":
      return {
        items: state.items.map((i) =>
          i.id === action.id ? { ...i, qty: Math.max(1, action.qty) } : i
        ),
      };
    case "remove":
      return { items: state.items.filter((i) => i.id !== action.id) };
    default:
      throw new Error(`Unknown action: ${action.type}`);
  }
}

Questions I ask about this reducer:

1. Why return a new object instead of pushing
   into state.items?
   (React compares references; mutation can skip
   re-renders and breaks predictable updates.)

2. Why Math.max(1, action.qty)?
   (Quantity should never be zero or negative;
   removing is a separate action.)

3. Why throw in the default case?
   (A typo in an action type fails loudly instead
   of silently doing nothing.)

An author answers these in seconds. A copier
usually knows what the code does but not why.

// 1. New reducer case
case "clear":
  return initialCart;

// 2. Derived total, no extra state
const total = cart.items.reduce(
  (sum, i) => sum + i.price * i.qty,
  0
);

// 3. Formatting for Indian rupees
const label = new Intl.NumberFormat("en-IN", {
  style: "currency",
  currency: "INR",
}).format(total);

// 4. Wiring in the component
const onClear = () => dispatch({ type: "clear" });

'The cart lives in a useReducer in CartProvider,
so clearing it is a new action. I will add a
"clear" case that returns initialCart.

For the total, I will not add state, because it
can be calculated from items. Storing it would mean
keeping two things in sync.

I will format it with Intl.NumberFormat for INR.'

Even before typing, this narration tells me the
candidate knows where everything lives.

STEP 1: REBUILD FROM MEMORY
  Close the tutorial. Rebuild the core feature
  in a fresh Vite project without looking.
  Note every place you got stuck.

STEP 2: ADD THREE FEATURES THE TUTORIAL DID NOT
  e.g. cart persistence, keyboard support,
  a filter that survives page refresh in the URL.

STEP 3: WRITE TESTS FOR YOUR LOGIC
  At least the reducer or data helpers.

Commit each step separately with clear messages.

## About this project
This started from a shopping cart tutorial.
I rebuilt it from scratch and added:
- Cart saved to localStorage and restored on load
- Quantity rules (minimum 1, max from stock)
- Keyboard-accessible cart drawer
- Unit tests for cartReducer (Vitest)

## Decisions
- useReducer over useState: cart has 4 actions
- Context only for cart; product data fetched per page

## Known limits
- No real checkout or payment

BEFORE THE INTERVIEW, CAN I...

[ ] Explain why every file exists?
[ ] Explain every dependency in package.json?
[ ] Name one bug I fixed and how?
[ ] Add a small feature live in under 10 minutes?
[ ] Explain one thing I would do differently?
[ ] Say honestly which parts came from a tutorial?

Any 'no' means more work before listing it.