async await メモ

sample

const af = async ()=>{
  setTimeout(()=>{
    console.log("anonymouse func")
  }, 500);
  const ret = await new Promise((resolve)=>{
    console.log("promise function");
    //return 123; // Invalid Code
    resolve(123);
  }).then(r=>{
    console.log(`r:${r}`)
    return r
  });
  console.log("end");
  return ret
}

console.log("before")
const ret = af()
console.log("after")
ret.then(r=>console.log(`r ${r}`));

result

> "before"
> "promise function"
> "after"
> "r:123"
> "end"
> "r 123"
> "anonymouse func"

memo

• async は非同期呼び出しを可能とする定義
• await は、Promise.resolveでラップした値を返す
• new Promise()に渡した関数は、引数のresolveに渡された値をPromiseでラップして返す
• Promise.then()は、resolveされた値を引数に取り、returnした値をPromiseでラップして返す

参考

https://developer.mozilla.org/ja/docs/Web/JavaScript/Reference/Statements/async_function
https://developer.mozilla.org/ja/docs/Web/JavaScript/Reference/Global_Objects/Promise
https://developer.mozilla.org/ja/docs/Web/JavaScript/Reference/Statements/async_function