MDN - Promise
https://developer.mozilla.org/ko/docs/Web/JavaScript/Reference/Global_Objects/Promise
MDN - Using Promise
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Using_promises
Captain Pangyo - 자바스크립트 Promise 쉽게 이해하기
https://joshua1988.github.io/web-development/javascript/promise-for-beginners/
가용한 시간은 한정적이고, 배울건 넘쳐난다.