js__typescript__pluralsight2/course/src/app.d.ts

// D.TS files only contain type definitions, no classes or functions.

// Interfaces with the same name and the same scope or namespace will just add
// to each other, not conflict as long as there are no member with conflicting
// types.

interface Window {
    psExpenses: string;
}

type CustomDragEvent = {
    posX: number;
    posY: number;
}

// Intersection types. Main difference from using an interface extending Event:
// the interface could be inherited later, while the type cannot (it's not a
// class).
type DragStartEvent = Event & { dragStart: CustomDragEvent };
type DragStopEvent = Event & { dragStop: CustomDragEvent };

// Interfaces are better for reusable signatures, while types aliases like those
// above are better for final single-use cases.
interface IDragStartEvent extends Event {
    dragStart: CustomDragEvent;
}
interface Foo extends IDragStartEvent {}