https://pygmalion0220.tistory.com/entry/%ED%94%84%EB%A1%9C%EA%B7%B8%EB%9E%98%EB%B0%8D-SessionStorage
1. (숫자).toString() : Object.prototype.toString 메서드를 활용하는 방법 출처: https://curryyou.tistory.com/186 [카레유:티스토리]