Astute readers might be wondering what happens when TypeScript programmers need to interface with JavaScript modules that have no type information. TypeScript recognizes files labelled *.d.ts as definition files. These files are meant to use TypeScript to describe interfaces presented by JavaScript libraries.

There are communities of people dedicated to creating typings for JavaScript projects. There is also a utility called typings (npm install --save-dev typings) that can be used to manage third party typings from a variety of sources. (Deprecated in TypeScript 2.0)

In TypeScript 2.0, users can get type files directly from @types through npm (for example, npm install --save @types/lodash will install lodash type file).

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