typescript multiple annotations code example

Example 1: typescript extends multiple types

interface You {
  name: string;
  value: number;
}

interface FooYou {
  name: 'foo';
}

interface ConcreteFooYou extends You, FooYou {
  concrete: boolean;
}

Example 2: typescript annotate return type

function add(x: number, y: number): number {
  return x + y;
}