TypeScript Open Source Projects
The language and its toolchain
Start here: these repos are the TypeScript ecosystem's own source code, and each demonstrates the lessons of this track at production scale.
| Project | What it is | Stars | What to study in the code |
|---|---|---|---|
| microsoft/TypeScript | The compiler, written in TypeScript | ~105k | The checker itself: src/compiler/checker.ts shows structural assignability implemented from first principles — every type lesson in one file |
| microsoft/vscode | The editor, a very large TS codebase | ~175k | How a million-line codebase organizes types: src/vs layering, strict const enum/interface conventions, dependency-injection by type |
| microsoft/TypeScript-Website | The handbook and playground | ~2.5k | The handbook's source — compare its explanations to what you learned here, then improve one page as a first contribution |
| typescript-eslint | ESLint with type-aware rules | ~16k | Rules that use the type checker at lint time; how the AST differs from plain JavaScript linting |
Frameworks and application code
These show how the type system shapes architecture — routing, DI, and module boundaries done with types rather than runtime magic.
| Project | What it is | Stars | What to study in the code |
|---|---|---|---|
| vitejs/vite | The dominant web build tool and dev server | ~78k | packages/vite/src/node: plugin typing, config inference, the moduleResolution: "Bundler" world from the compiler lesson in action |
| nestjs/nest | Batteries-included Node framework | ~72k | Decorators and metadata reflection (packages/core) — the legacy-decorator lesson at framework scale |
| remix-run/react-router | Router for React (TypeScript-first) | ~55k | Typed route params and useLoaderData-style inference: type-safe APIs over dynamic URL strings |
| withastro/astro | Content-first web framework | ~52k | How a framework ships types users never write: generated route types and content collections |
Type-heavy libraries
These libraries are famous for what their types do — reading their declaration files is a course in itself.
| Project | What it is | Stars | What to study in the code |
|---|---|---|---|
| colinhacks/zod | Schema validation with inferred types | ~42k | How one runtime schema produces both validation and static types — the "parse, don't validate" lesson, industrialized |
| TanStack/query | Async state management | ~47k | Aggressive generic inference: query keys, results, and error types flow through without annotations |
| axios/axios | HTTP client | ~108k | Overload sets on the request functions — the functions lesson's overload section at real scale |
| prisma/prisma | Type-safe ORM and client generator | ~44k | Generated types from a schema language: the endgame of "one source of truth" typing |
| date-fns/date-fns | Date utility library | ~36k | Overloads and generic options types that keep tree-shaking-friendly functions fully typed |
How to study a repository
Cloning a 100k-star repo and reading top-to-bottom is a waste of a week. Work in this order instead.
Start at the type surface
Open the package's .d.ts entry (or dist/types) in your editor and read only the exported signatures — no bodies. You are reading the library's API as its authors framed it: what is generic, what is a union, what is readonly. This is the design-time half from the compiler lesson, isolated.
Pick one function and follow it
Choose the smallest exported function you actually use. Set a breakpoint, step through, and keep a note each time a runtime check pairs with a type construct you recognize — that pairing is exactly what the checker cannot see and the code must verify. It is the why-typescript lesson made concrete.
Read the tsconfig, not just the code
Each repo's tsconfig records its trade-offs: strictness level, target, module strategy. Compare microsoft/TypeScript (conservative, self-hosting) with vite (modern, bundler-oriented). You will find real projects disagreeing about the same flags from the setup lesson — disagreement is information.
Make one pull request
The lab's exit criterion: one merged or open PR in any of these repos — a doc fix, a type narrowing in a test, a better error message. TypeScript-Website and typescript-eslint are the friendliest entry points; a typed fix to a handbook page still counts, because the point is finishing the loop from reader to contributor.