> For the complete documentation index, see [llms.txt](https://sudevgeny.gitbook.io/typescript/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://sudevgeny.gitbook.io/typescript/type-system/intro.md).

# Декларирование среды

As we mentioned in [why TypeScript](/typescript/getting-started/why-typescript.md):

> A major design goal of TypeScript was to make it possible for you to safely and easily use existing JavaScript libraries in TypeScript. TypeScript does this by means of *declaration*.

Ambient declarations allow you to *safely use existing popular JavaScript libraries* and *incrementally migrate your JavaScript/CoffeeScript/Other-Compile-To-Js-Language project to TypeScript*.

Studying patterns in ambient declarations for *third party JavaScript code* is good practice for annotating *your* TypeScript code base as well. This is why we present it so early on.