May 2019
Intermediate to advanced
464 pages
9h 22m
Japanese
Content preview from Node.jsデザインパターン 第2版
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86
4
章
ES2015
以降の機能を使った非同期パターン
❷
エラーが発生した場合、プロミスを
reject
する。さらに、コールバックが提供されている場合は、
そちらにもエラーを通知する
❸
計算が終わればプロミスを
resolve
する。さらに、コールバックが提供されている場合は、そち
らにも処理結果を通知する
このモジュールはコールバックベースの
API
としても、プロミスベースの
API
としても利用できます。
使用例を見ましょう（
05_exposing_callback_and_promises/test.js
）。
//
コールバックベースの
API
として使用
asyncDivision(10, 2, (error, result) => {
if (error) {
return console.error(error);
}
console.log(result);
});
//
プロミスベースの
API
として使用
asyncDivision(22, 11)
.then(result => console.log(result))
.catch(error => console.error(error))
;
このように少しの工夫で、
API
の利便性が向上します。ユーザーは自身のニーズに合った使い方が
でき、プロミス化の手間が省けるのです。
4.2
ジェネレータ
ES2015
ではプロミス以外にも、非同期の制御フローを簡単に記述するための機構として「ジェネレー
タ（
generator
）」も提供されています（ジェネレー ...
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O’Reilly covers everything we've got, with content to help us build a world-class technology community, upgrade the capabilities and competencies of our teams, and improve overall team performance as well as their engagement.Julian F.
I wanted to learn C and C++, but it didn't click for me until I picked up an O'Reilly book. When I went on the O’Reilly platform, I was astonished to find all the books there, plus live events and sandboxes so you could play around with the technology.Addison B.
I’ve been on the O’Reilly platform for more than eight years. I use a couple of learning platforms, but I'm on O'Reilly more than anybody else. When you're there, you start learning. I'm never disappointed.Amir M.
I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.