Introduction

This is where TypeScript "cheats" and ships with a file called lib.d.ts. This file contains ambient declarations for a whole bunch of common JavaScript constructs present in JavaScript runtimes and the DOM.

• This file is automatically included in the compilation context of a TypeScript project.
• The objective of this file is to make it easy for you to start writing type checked JavaScript code.

Modifying Native Types

If you want to be a clever clogs you can add stuff to the interfaces in lib.d.ts by creating a global module (ie: global.d.ts)

Example

lib.d.ts magic

The following code is only possible because of lib.d.ts. If it's used with the nolib option, TypeScript doesn't know that all JavaScript objects have a toString function.

var foo = 123;
var bar = foo.toString();

Example of what's in the lib.d.ts

declare var window: Window

interface Window
  extends EventTarget,
    WindowTimers,
    WindowSessionStorage,
    WindowLocalStorage,
    WindowConsole,
    GlobalEventHandlers,
    IDBEnvironment,
    WindowBase64 {
  animationStartTime: number
  applicationCache: ApplicationCache
  clientInformation: Navigator
  closed: boolean
  crypto: Crypto
  // so on and so forth...
}

Related

• TypeScript