What is TypeScript and what problems does it solve?

Summary

TypeScript is a statically typed superset of JavaScript that adds a type system and compiles (by erasing types) to plain JavaScript. It catches type errors at compile time, improves editor tooling and documents intent in large codebases.

Longer Answer

Any valid JavaScript is (almost always) valid TypeScript. The type checker (tsc) analyses code without running it; types are erased in the output, so there's no runtime type checking. Benefits include safer refactors, autocompletion, self-documenting APIs and catching undefined is not a function bugs before production. Tools like esbuild, SWC and Node's type stripping can remove types without checking them, so teams run tsc --noEmit separately in CI.

Key Points

• Superset of JavaScript
• Static checking, types erased at compile time
• No runtime type validation
• Better tooling and refactoring

What interviewers look for

Understanding that types disappear at runtime, which is why external data still needs validation (e.g., Zod).

Follow-up questions

• How do you validate API responses at runtime in a TypeScript app?