TypeScript

TypeScript is a programming language developed by Microsoft that adds an optional static type system to JavaScript. Code is written with type annotations, checked by the compiler, and then compiled to plain JavaScript that runs anywhere JavaScript runs, since the types exist only at build time. Because every valid JavaScript file is also valid TypeScript, existing projects can adopt it incrementally. The benefit is catching a class of errors before execution, such as passing the wrong shape of object or reading a property that may be undefined, and the same type information powers editor features like accurate autocomplete, safe renaming, and inline documentation. Those benefits grow with codebase and team size, which is why most large frontend and Node projects now default to it. React, Next.js, Vue, and Angular all ship type definitions, and libraries such as Zod validate runtime input while inferring matching static types. Runtimes including Deno and Bun, and recent Node versions, can execute TypeScript files directly. The common pitfall is defeating the system with the any type or unchecked type assertions, which silence the compiler while leaving the original bug in place, and types guarantee nothing about data arriving from an API unless it is validated at the boundary.