TypeScript Interview Questions

TypeScript is a statically-typed superset of JavaScript developed by Microsoft that compiles down to plain JavaScript. It adds optional static type annotations, interfaces, generics, and other tooling-friendly features on top of JavaScript's existing runtime semantics. It solves several problems that plain JavaScript has: (1) Type-related bugs (e.g., calling a method that doesn't exist on a value, passing a string where a number is expected) are caught at compile time instead of at runtime in production. (2) Large codebases become harder to refactor safely in plain JS because there's no static contract describing what shape an object or function argument should have - TypeScript's type checker catches broken call sites immediately after a refactor. (3) Editor tooling (autocomplete, inline documentation, 'go to definition', rename-symbol) is dramatically better with static types, since the IDE can reason about exact shapes of objects and function signatures. Because TypeScript is a superset, any valid JavaScript is (almost always) valid TypeScript, so adoption can be incremental. It's a purely compile-time/type-checking layer - the type annotations are erased during compilation, so it has no effect on runtime behavior or performance.