Learn TypeScript 3 by Building Web Applications

Defining the controller contract

Create a file called world-explorer-controller.intf.ts under src/controllers.

Here's the interface definition:

export interface WorldExplorerController { 
    loadCountries(): Promise<void>; 
    loadYears(): void; 
    renderChart(): void; 
} 

This interface is fairly basic but will take care of everything we need.