fix: use function overload

Author: soliyn

apps/typescript/15-function-overload/src/app/app.component.ts

@@ -9,7 +9,7 @@ import { createVehicle } from './vehicle.utils';
 export class AppComponent {
  car = createVehicle('car', 'diesel');
  moto = createVehicle('moto', 'diesel');
- bus = createVehicle('bus', undefined, 20);
- boat = createVehicle('boat', undefined, 300, true);
+ bus = createVehicle('bus', 20, true);
+ boat = createVehicle('boat', 300);
  bicycle = createVehicle('bicycle');
 }

apps/typescript/15-function-overload/src/app/vehicle.utils.ts

@@ -28,28 +28,39 @@ interface Boat {
 
 type Vehicle = Bicycle | Car | Moto | Bus | Boat;
 
+export function createVehicle(type: 'bicycle'): Bicycle;
+export function createVehicle(type: 'car', fuel: Fuel): Car;
+export function createVehicle(type: 'moto', fuel: Fuel): Moto;
+export function createVehicle(
+ type: 'bus',
+ capacity: number,
+ isPublicTransport: boolean,
+): Bus;
+export function createVehicle(type: 'boat', capacity: number): Boat;
 export function createVehicle(
  type: VehicleType,
- fuel?: Fuel,
- capacity?: number,
+ fuelOrCapacity?: Fuel | number,
  isPublicTransport?: boolean,
 ): Vehicle {
  switch (type) {
  case 'bicycle':
  return { type };
  case 'car':
  case 'moto':
- if (!fuel) throw new Error(`fuel property is missing for type ${type}`);
- return { fuel, type };
+ if (!fuelOrCapacity || !isFuel(fuelOrCapacity))
+ throw new Error(`fuel property is missing for type ${type}`);
+ return { fuel: fuelOrCapacity, type };
  case 'boat':
- if (!capacity)
+ if (!fuelOrCapacity || isFuel(fuelOrCapacity))
  throw new Error(`capacity property is missing for type boat`);
- return { capacity, type };
+ return { capacity: fuelOrCapacity, type };
  case 'bus':
- if (!capacity)
+ if (!fuelOrCapacity || isFuel(fuelOrCapacity))
  throw new Error(`capacity property is missing for type bus`);
  if (!isPublicTransport)
  throw new Error(`isPublicTransport property is missing for type bus`);
- return { capacity, isPublicTransport, type };
+ return { capacity: fuelOrCapacity, isPublicTransport, type };
  }
 }
+
+const isFuel = (fuel: Fuel | number): fuel is Fuel => typeof fuel !== 'number';