Best TypeScript Open Source Repositories

TypeScript is a statically typed superset of JavaScript developed by Microsoft: any valid JavaScript is also valid TypeScript, and the TypeScript compiler adds a type system on top, catching type-related bugs, like calling a function with the wrong argument type, at compile time rather than letting them surface as runtime errors. TypeScript compiles down to plain JavaScript, so it can run anywhere JavaScript runs, in browsers or in Node.js, with the type annotations stripped out during the build step and used only to catch problems during development.

Its type system supports advanced features like generics, union types, and type inference, which let developers get strong typing benefits without annotating every single variable explicitly. For large codebases with many contributors, this catches an entire class of bugs before code ships and makes refactoring safer, since the compiler flags places where a change breaks an assumption elsewhere in the code, something plain JavaScript can't offer without extensive test coverage to catch the same issues at runtime instead.

TypeScript has become the default choice for serious front-end and full-stack JavaScript projects, particularly ones maintained by larger teams or with long-term maintenance in mind. Given how broadly it's been adopted, TypeScript appears across a huge share of the repos on this page: React, Next.js, VS Code, Supabase, Playwright, and Prisma are all written primarily in TypeScript, along with UI libraries like Material UI and shadcn/ui, and infrastructure tools like Grafana and Prisma's ORM tooling.