# Декларирование среды

As we mentioned in [why TypeScript](https://sudevgeny.gitbook.io/typescript/getting-started/why-typescript):

> 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.