Ambient Namespaces

Ambient Namespaces

The popular library D3 defines its functionality in a global object called d3. Because this library is loaded through a <script> tag (instead of a module loader), its declaration uses namespaces to define its shape. For the TypeScript compiler to see this shape, we use an ambient namespace declaration. For example, we could begin writing it as follows:

D3.d.ts (simplified excerpt)

declare namespace D3 {
  export interface Selectors {
    select: {
      (selector: string): Selection;
      (element: EventTarget): Selection;
    };
  }

  export interface Event {
    x: number;
    y: number;
  }

  export interface Base extends Selectors {
    event: Event;
  }
}

declare var d3: D3.Base;