Penjaga Tipe

function isString(value: unknown): boolean {
  return typeof value === "string";
}

function printLength(value: unknown): void {
  if (isString(value)) {
    console.log(value.length); 
// TypeScript knows 'value' is a string here
  } else {
    console.log("Value is not a string");
  }
}

printLength("Hello"); 
// Output: 5
printLength(42); 
// Output: Value is not a string

function printValue(value: string | number): void {
  if (typeof value === "string") {
    console.log(`String value: ${value}`);
  } else {
    console.log(`Number value: ${value}`);
  }
}

printValue("Hello"); 
// Output: String value: Hello
printValue(42); 
// Output: Number value: 42

class Dog {
  bark(): void {
    console.log("Woof!");
  }
}

class Cat {
  meow(): void {
    console.log("Meow!");
  }
}

function makeSound(animal: Dog | Cat): void {
  if (animal instanceof Dog) {
    animal.bark();
  } else {
    animal.meow();
  }
}

let dog = new Dog();
let cat = new Cat();
makeSound(dog); 
// Output: Woof!
makeSound(cat); 
// Output: Meow!

interface Car {
  make: string;
  model: string;
}

interface Bike {
  brand: string;
  type: string;
}

function isCar(vehicle: Car | Bike): vehicle is Car {
  return (vehicle as Car).make !== undefined;
}

function printVehicle(vehicle: Car | Bike): void {
  if (isCar(vehicle)) {
    console.log(`Car: ${vehicle.make} ${vehicle.model}`);
  } else {
    console.log(`Bike: ${vehicle.brand} ${vehicle.type}`);
  }
}

let car: Car = { make: "Toyota", model: "Corolla" };
let bike: Bike = { brand: "Yamaha", type: "Sport" };

printVehicle(car); 
// Output: Car: Toyota Corolla
printVehicle(bike);
 // Output: Bike: Yamaha Sport

interface Circle {
  kind: "circle";
  radius: number;
}

interface Rectangle {
  kind: "rectangle";
  width: number;
  height: number;
}

type Shape = Circle | Rectangle;

function calculateArea(shape: Shape): number {
  if (shape.kind === "circle") {
    return Math.PI * shape.radius ** 2;
  } else {
    return shape.width * shape.height;
  }
}

let circle: Circle = { kind: "circle", radius: 5 };
let rectangle: Rectangle = { kind: "rectangle", width: 10, height: 20 };

console.log(calculateArea(circle)); 
// Output: 78.53981633974483
console.log(calculateArea(rectangle)); 
// Output: 200

function getShapeInfo(shape: Shape): string {
  switch (shape.kind) {
    case "circle":
      return `Circle with radius ${shape.radius}`;
    case "rectangle":
      return `Rectangle with dimensions ${shape.width}x${shape.height}`;
    default:
      // This line ensures all cases are handled
      const _exhaustiveCheck: never = shape;
      return _exhaustiveCheck;
  }
}