Discriminated Unions in Typescript

du-interfaces_initial.ts

enum CarTransmission {
  Automatic = 200,
  Manual = 300
}

interface IMotorcycle {
  vType: "motorcycle"; // discriminant
  make: number; // year
}

interface ICar {
  vType: "car"; // discriminant
  transmission: CarTransmission
}

interface ITruck {
  vType: "truck"; // discriminant
  capacity: number; // in tons
}