Why should you care?

Types catch typos before runtime and document API contracts between frontend and backend teams.

See it live — copy this example

Paste into your MeanVerse project (Angular + Express + MongoDB), then run with ng serve / node / mongosh as noted.

type AccountType = 'checking' | 'savings';

interface Account {
  id: string;
  name: string;
  balance: number;
  type: AccountType;
}

function isOverdrawn(acct: Account): boolean {
  return acct.balance < 0;
}

What happened?

• interface describes object shape.
• Union type AccountType limits values to two strings.
• Function params and return types are checked at compile time.

Practice next

1. Enable strict in tsconfig.json.
2. Convert one JS file to TS with explicit param types.
3. Fix red squiggles from strict null checks.
4. Add readonly to Account id field.
5. Use satisfies operator for config objects.

Remember

TypeScript = JavaScript plus static types. Interfaces document MeanVerse domain models. strict mode finds more bugs early.

API contract clarity

Backend changes balance to string by mistake.

Outcome: Angular build fails until types align — bug never reaches QA.