TypeScript Interview Questions (2026) — 15 Real Questions + AI Mock Interview
TypeScript interviews test whether you can use the type system to make code safer, not just bolt types onto JavaScript. Expect questions on type vs interface, generics, narrowing, and utility types for frontend and full-stack roles, often alongside JavaScript fundamentals and a coding round. In 2026 TypeScript is the default for serious frontend teams. Below are the questions asked most, with what a senior interviewer is grading for.
15 TypeScript interview questions you'll actually get asked
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1. What does TypeScript give you over plain JavaScript?
How a senior interviewer scores this: Compile-time safety, better tooling/refactoring, self-documenting contracts — not runtime behaviour changes.
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2. type vs interface — when do you use each?
How a senior interviewer scores this: Interfaces for extendable object shapes; types for unions, primitives, and mapped types.
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3. any vs unknown vs never.
How a senior interviewer scores this: any disables checking; unknown forces narrowing before use; never is the unreachable/empty type.
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4. Explain generics with a real example.
How a senior interviewer scores this: Writes a reusable generic function/type and uses constraints (extends) appropriately.
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5. How does type narrowing / type guards work?
How a senior interviewer scores this: Uses typeof, instanceof, in, and custom 'x is T' predicates to refine types.
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6. Enums vs union literal types.
How a senior interviewer scores this: Prefers union literals for tree-shaking and simplicity; knows enum runtime cost.
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7. What are utility types like Partial, Pick, Omit, Record?
How a senior interviewer scores this: Knows what each produces and composes them instead of redefining shapes.
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8. Explain structural typing.
How a senior interviewer scores this: Compatibility is by shape, not name; understands why an excess-property check exists on literals.
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9. When are type assertions dangerous?
How a senior interviewer scores this: `as` bypasses the checker; uses it sparingly and prefers narrowing or generics.
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10. What is a discriminated union and why use it?
How a senior interviewer scores this: A shared literal 'tag' lets the compiler narrow exhaustively; pairs it with never for exhaustiveness.
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11. Optional chaining and nullish coalescing — what do they solve?
How a senior interviewer scores this: ?. short-circuits on null/undefined; ?? differs from || by not catching falsy 0/''.
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12. What do readonly and `as const` do?
How a senior interviewer scores this: Immutability at the type level; as const narrows to literal types and freezes structure.
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13. What are declaration files (.d.ts) for?
How a senior interviewer scores this: Describe types for untyped JS; knows DefinitelyTyped / @types packages.
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14. Why turn on strict mode / strictNullChecks?
How a senior interviewer scores this: Catches null/undefined bugs at compile time; sees it as essential, not optional.
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15. How do conditional and mapped types work at a high level?
How a senior interviewer scores this: T extends U ? X : Y and key remapping; doesn't need to be fluent but should grasp the idea.
How TypeScript answers are scored
Strong candidates aren't just correct — they're graded on five dimensions a real interviewer weighs: technical correctness, communication, problem-solving, depth, and culture fit. For TypeScript specifically, the fastest score jump is narrating your reasoning and trade-offs out loud before you write code. Each question above lists what the interviewer is actually listening for.
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TypeScript interview FAQ
What level are these TypeScript interview questions for?
Junior through senior frontend and full-stack roles. Screens cover type vs interface and basic generics; senior loops add advanced generics, narrowing, and utility-type composition. Strong JavaScript fundamentals are assumed underneath.
Do I need JavaScript fundamentals too?
Yes. TypeScript interviews almost always include JavaScript questions — closures, the event loop, async — because TS compiles to JS. Treat TS as a layer on top, and prepare both the type system and the runtime.
How should I prepare for a TypeScript interview in 2026?
Practise designing types for real data, not toy examples — model an API response with unions and utility types. Be ready to explain narrowing and why strictNullChecks matters, out loud and with examples.