TypeScript

Unlike most languages that compile to JavaScript, TypeScript is a strict superset — any valid JavaScript file is already valid TypeScript. Microsoft released it in October 2012, and it has since become the default choice for typed JavaScript development. The compiler adds a structurally typed type system that resolves types at compile time and erases them completely before emitting JavaScript, adding zero runtime overhead.

TypeScript tracks the TC39 specification process closely and regularly ships stage-3 ECMAScript proposals ahead of browser support. The compiler doubles as a language server: the same analysis that catches type errors drives autocompletion, refactoring, and go-to-definition in VS Code, JetBrains, and any LSP-capable editor. The current stable release is TypeScript 5.9. A Go-based rewrite of the compiler is in active development as TypeScript 7, targeting roughly 10x faster type-checking.

The official handbook remains the best starting point. For deeper type-system understanding, the community-maintained type challenges repository provides progressive exercises from beginner to expert level.