https://okayoon.tistory.com/entry/%EC%95%84%ED%8B%B0%ED%81%B4-%ED%94%84%EB%A1%9C%EC%A0%9D%ED%8A%B8-058-%EC%A6%89%EC%8B%9C-%EC%8B%A4%ED%96%89-%ED%95%A8%EC%88%98-IIFE-Immediately-Invoked-Function-Expression
