type 선언 중 | 가 먼저 나오는 건 대체 뭐야

type Shape =
  | { kind: "circle"; radius: number }
  | { kind: "square"; sideLength: number };
 
function area(shape: Shape): number {
  const isCircle = shape.kind === "circle";
  if (isCircle) {
    // We know we have a circle here!
    return Math.PI * shape.radius ** 2;
  } else {
    // We know we're left with a square here!
    return shape.sideLength ** 2;
  }
}

type Shape = 
| { kind: "circle"; radius: number }
| { kind: "square"; sideLength: number };
// 위의 코드는 아래와 같다

type Shape = { 
  kind: "circle";
  radius: number;
} | {
  kind: "square";
  sideLength: number;
}