Why TypeScript? — quiz

A Cypress test reads cy.get(`[data-testid="${user.userName}"]`) but the API returns the field as `username` (lowercase n). The test silently fails to find the element on every run. Which TypeScript feature would have caught this BEFORE the test ran?

• Strict null checks would have caught the casing mismatch
• Property access checking via interfaces — TypeScript flags `user.userName` as a compile error if the User interface declares `username`
• Runtime type validation built into the language
• Type inference on numeric values