ternary operator
{showing === true ? <Header>Header</Header> : null}
https://codingbroker.tistory.com/74
babel-polyfill
http://blog.naver.com/PostView.nhn?blogId=naan_ace&logNo=221681526607&parentCategoryNo=20&categoryNo=&viewDate=&isShowPopularPosts=false&from=postView