callback

https://six605.tistory.com/196#:~:text=%2D%20callback%20%ED%95%A8%EC%88%98%EB%8A%94%20%EB%B6%88%EB%A0%A4%EC%A7%80%EB%8A%94,%ED%95%A8%EC%88%98%EA%B0%80%20callback%20%ED%95%A8%EC%88%98%EC%9D%B4%EB%8B%A4.