async / await
JavaScript Promiseの本
https://azu.github.io/promises-book/#_書籍の目的
async/await 入門(JavaScript)
https://qiita.com/soarflat/items/1a9613e023200bbebcb3
Promiseとasync-awaitの例外処理を完全に理解しよう
https://web.archive.org/web/20171227042008/https://qiita.com/gaogao_9/items/40babdf63c73a491acbb