איגודים וצמצום

let result: number | string;
result = 42; // Valid
result = 'Error 404'; // Valid

function printLength(value: string | number) {
  if (typeof value === 'string') {
    // TypeScript knows 'value' is a string here
    console.log(value.length);
  } else {
    // TypeScript knows 'value' is a number here
    console.log(value.toFixed(2));
  }
}

interface Fish {
  swim: () => void;
}
interface Bird {
  fly: () => void;
}

function move(animal: Fish | Bird) {
  if ('swim' in animal) {
    animal.swim(); // Narrowing to Fish
  } else {
    animal.fly(); // Narrowing to Bird
  }
}

interface SuccessResponse {
  status: 'success'; // Literal discriminator
  data: string;
}

interface ErrorResponse {
  status: 'error'; // Literal discriminator
  errorMessage: string;
}

type ApiResponse = SuccessResponse | ErrorResponse;

function handleResponse(response: ApiResponse) {
  if (response.status === 'success') {
    console.log('Data received:', response.data);
  } else {
    console.error('An error occurred:', response.errorMessage);
  }
}