TypeScript Interview Questions

This is the first question every TypeScript developer should be able to answer. It reveals whether they've thought about when to use each, or just default to one out of habit.

Type narrowing is how TypeScript actually prevents bugs at runtime. Candidates who use `as` casts instead of proper guards are just silencing the compiler, not fixing the problem.

The `any` vs `unknown` choice is a direct signal of how seriously a developer takes type safety. Candidates who default to `any` will spread type holes through your entire codebase.

TypeScript errors can be intimidating. This shows whether the candidate can read error messages methodically and trace the root cause, or just adds `as any` until the red squiggles disappear.

Enums have hidden runtime costs that many developers don't know about. Candidates who know about `as const` alternatives show they care about bundle size and understand what TypeScript compiles to.

TypeScript's power comes from its tooling integration. A developer who uses hover types, rename symbol, and typescript-eslint catches bugs in the editor instead of in code review.

Discriminated unions are one of TypeScript's most powerful patterns for modeling real domain data. A candidate who can build one understands how to make illegal states unrepresentable.