Ambient Declarations

As we mentioned in 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/Others-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.