DefinitelyTyped

DefinitelyTyped is a community-driven repository of TypeScript type definitions for JavaScript libraries. It provides ambient TypeScript declaration files (.d.ts) that enable type checking and editor autocompletion for libraries that do not ship their own typings. The typings published through DefinitelyTyped are installed via npm under the @types scope (for example, npm i --save-dev @types/lodash), allowing TypeScript projects to use third‑party packages with accurate type information.

The project is hosted on GitHub as DefinitelyTyped/DefinitelyTyped and is maintained by volunteers in collaboration with the TypeScript team. It started to address the lack of typings for popular JavaScript libraries and has since become the de facto source for community-maintained typings. Each library commonly has its own folder containing an index.d.ts and, in some cases, tests and compatibility notes. Typings describe the library’s API surface and are periodically updated to reflect new library versions and TypeScript versions.

Contributions are made through pull requests and go through review and automated checks. Tools such as types-publisher are used to publish new typings to npm under the @types namespace. The typings in DefinitelyTyped are not official library releases; authors may choose to provide their own typings, or rely on DefinitelyTyped when the library itself does not ship definitions. TypeScript projects automatically benefit from these typings, improving safety and developer experience when consuming JavaScript libraries.

Overall, DefinitelyTyped has had a significant impact on the TypeScript ecosystem by supplying a centralized, community-maintained source of typings for thousands of libraries. The project operates under an open collaboration model and, in practice, complements library authors’ own typings where available.